Kellyroach/upgrade to xcode10

[kellyroach]

This pull request updates AJParticlesLoadingView to Xcode 10 / Swift 4.2 .

• Add .gitignore
• Update to Xcode 10 / Swift 4.2
• Main.storyboard constraints improved.
• "Universal" to get better demo app appearance on iPad.
• START/STOP was always the same demo: heart - Fireflies .
  Revised demo app btnClicked chooses particle image and effect at random for
  more variety.
• START/STOP button background is now green/red .
• Rotating demo app to landscape looks OK enough.
• Deployment Target = 8.0
• Added AppIcon to demo app.

UPDATE: We've added another commit that moves the ambition of the P.R. back a bit
to Xcode 9, 9.3 / Swift 4.0 support. We're still hitting most of the bullet points listed
in the P.R. description above.

[arpitjain03]

Hi Kelly,
I will highly appreciate the work you have done for my library.
But the changes you have made, giving error in Xcode 9.4.

Thanks