Add an upload preview table with column type selectors

[waxlamp]

This uses @jtomeck's design for a preview table within a stepper to (1) select a CSV file to upload and (2) examine a sample of the data and set up column data types before (3) uploading the table to Multinet.

@jtomeck: I need help making my use of Vuetify have the right styles to match up to your design. For example:

• the colors are wrong
• the <v-select>s look ugly as sin
• no finish flag in the stepper
• the stepper got reduced to only two steps

Let me know what you think.

Closes #134

[jtomeck]

I just made a commit improving some of the look and styles. For some reason the table scrolling is not working properly. That went away when I removed the padding of the stepper content around the table. Do any of you see anything that could be wrong? If not I can remove the padding and it should resolve itself, I just like the look better without the padding. @waxlamp @AlmightyYakob

[waxlamp]

I just made a commit improving some of the look and styles. For some reason the table scrolling is not working properly. That went away when I removed the padding of the stepper content around the table. Do any of you see anything that could be wrong? If not I can remove the padding and it should resolve itself, I just like the look better without the padding. @waxlamp @AlmightyYakob

I think this looks great, @jtomeck.

I know there's a problem with scrolling--can we file an issue and fix that as it causes problems later?