Fix several tiny CSS bugs

Closes #4050

- Full-width invite user modal button
- `<select>` can be focused in Firefox
- Increase size of background images for avatars
- Add `-moz-osx-font-smoothing: grayscale;` to icons
Correctly close PSM

closes #4077
- Swap CSS toggling for new PSM closing method
Merge pull request #4079 from halfdan/4077-close-psm

Correctly close PSM
Merge pull request #4053 from PaulAdamDavis/css-bug-fixes

Tiny CSS bug fixes
Change HTML email link to hide token

closes #3305
- Hide token in HTML email
Naming cleanup

closes #4069
- Rename everything from camelCase to lowercase + dashes
- Remove usage of `server`, `app` and `instance`
Meta data screen

closes #3939
- Add Seo Tab component to PSM
- Add new gh-blur-textarea component
- Refactor blur-input to use new text-input mixin
Merge pull request #4066 from halfdan/3939-psm3-meta

Meta data screen
Fixes sass:compress

no ref
- Use absolute path for compress/sourceMap
Merge pull request #4092 from halfdan/fix-sass

Fixes sass:compress
Merge pull request #4081 from halfdan/3305-derp

Change HTML email link to hide token
Merge pull request #4074 from halfdan/4069-rename

Naming cleanup
Add checks for packages and contentPath to startup

Refs #3864
- Make sure that require() is able to resolve all dependencies
  listed in package.json.  If packages are missing halt the
  bootstrap process and display an error and help message for user.
- Check that contentPath and its subdirectories exist with the correct
  permissions.
- Check sqlite3 database file is set for read/write access.