Form validation on modal

#8
• Styled form error states and messages in credential modal
• Error logic for “branch” input is worked out, but not for the first
two inputs
• Added a help button to the API Key label. If clicked upon, the user
is taken to the github blog post about API keys.
• Squished the width of the modal down a bit
• Changed the color of the text input borders on focus to a dark grey
so that the red error states stand out more
• Increased the min-height of the milestone containers so that’s easier
to drag and drop issues into them when they’re empty
Fixed data branch helper message

And a few other CSS chingaz
Hook up the error states for the credentials dialog

- Validate token can be used to call github API
- Validate repo actually exists on github
- Change logic of when to show branch creation instructions

It's starting to look beautimous
Merge pull request #9 from benweatherman/validation-station

Validation station