Style changes

[jornane]

This pull request will make the following changes:

• Remove window borders and add a style to the header
• Larger font size
• Fewer hardcoded sizes
• Window is now resizeable
• Prevent some rare crashes when the user clicks on random things
• Better focus flow
• Search for institution and press Enter to select first match
• Rightclick contact details to copy them
• Disable Next button on institution search when no institution selected
• Make disabled buttons a lighter color
• Pressing enter on username field moves focus to password field
• Pressing backspace or the physical browser back button (some keyboards have that) will go to the previous screen
• GUI element borders are pixel aligned

Screenshots (before, after)