Introduce and use Theme singleton

[jarolrod]

Replaces #109

This introduces a Theme singleton which contains color definitions so that colors can be used by name instead of by hex. Additionally, it adjusts color definitions depending on if the gui is in dark or light mode.

Color definitions are based on our color palettes as defined in our design system:

A convenient demo of the changes can be found here: theme singleton demo

This demo adds a ThemeToggleButton so that we can toggle between light and dark. Uses the moon and sun icon from BitcoinIcons.

[shaavan]

Concept ACK

• The Theme.qml file and qmldir file are introduced correctly.

I was able to find some corrections that will help improve this PR.

Places where Theme singleton could be used:

• In ContinueButton.qml file. color: "white"
• In OptionSwitch.qml file. color: "#ffffff"

If I am mistaken, and the above colors should remain unchanged with dark mode toggling, I would suggest adding a non-changing white color variant in Theme.qml file as well and using it.

[GBKS]

Agree with @shaavan's suggestion. There are just a couple of places where I think we want to have a consistent color across both themes, the inactive toggle state being one of them.

I updated the Figma file with a "Static white" color and applied to the toggle. Let me know if you see other places to update this, and other colors to add.

[jarolrod]

Updated from (pr114.01 -> pr114.02, compare) to address review feedback. Then, updated from 7698dca to 581961a (pr114.02 -> pr114.03, compare) to fix trailing whitespace, or so I thought I had fixed it. Finally, updated from 581961a to 44a7696 (pr114.03 -> pr114.04, compare) to finally fix the linter.

The main diff to review is between pr114.01 and pr114.02

Changes: incorporate review feedback from @shaavan and @GBKS

• Address two instances where components were not using the theme definitions
• The color definitions were in fact flipped. Addressed the flipped definitions and adjusted the colors called by controls/components to fit inline with the specifications of the main design file.
• Introduced a white color definition to work as a static white color. This is to be used in places where the color white should not switch as it does with the definition of the color neutral0.

Additionally, the demo has been updated in order to display all components that we have which in turn incorporate all of the controls we have. This allows for convenient testing that the color definitions are as they should be. The demo can be found here: theme singleton demo

[shaavan]

Changes since my last review:

• Ordering of neutral0 - neutral9 is fixed.
• Added a static white color to the theme file and used it in the qml directory.

The arrangement of neutral0 - neutral9 is toggled and is now in line with the design system file.

I was able to verify that this PR is correctly formatted according to the clang format.

There is, however, one thing that needs to be addressed.

[jarolrod]

updated from 44a7696 to 9b9d198 (pr114.04 -> pr114.05, compare)

Changes: addressed @shaavan comments. Thank you for the eagle-eye review

[shaavan]

ACK 9b9d198

Changes since my last review:

• The color values for the dark and light themes for blue and purple have been fixed.

I successfully ran the theme singleton demo. I am attaching a few screenshots to show the correct working of this PR.

Screenshots:

	1	2
Light Theme
Dark Theme