Add custom websites to settings

Add setting which allows user to specify custom websites to include the
Toggl button on and which app they should be treated as. Requires
additional permission to "Read and modify all your data on the websites
you visit" rather than just the default list of websites.
Fix 2 bugs

Remove duplicate "Producteev" case, fix typo in "YouTrack" case.
Add new dynamic UI for websites on settings page

Add input and dropdown elements to eventually replace the textarea.
Since the new elements are not functional yet, I left the textarea in
place for the time being. The basic UI is there though, complete with
add and remove features. The form also pre-populates with the default
sites and their corresponding apps, which are pulled in from a JSON
object. The next step is to save the values from the new elements in
local storage to replace the textarea.
Add full functionality to new UI

Implement logic with new UI, remove old textarea UI. Websites in the
dynamic list now determine which websites the extension will actually
run on. Add button to restore to default websites. This is pretty much
good to go aside from a design review and maybe some UI tweaks.
Sync from upstream

Bringing in the new "nanny" changes.
Fix after sync, add checkbox, tweak settings CSS

Fix after sync from upstream, add checkbox for custom websites and logic
to use default websites if it is not checked, include Wunderlist in list
of apps, alphabetize app cases in switch, add confirmation box when
restoring custom websites to default, standardize HTML class names and
new request types to hyphens, clean up CSS styling on settings page.
Fix existing bug

Fix existing bug which always initializes checkboxes on settings page to
checked after the extension process is restarted. Previously, the `!!`
syntax would convert any non-empty, non-null string to `true`.
Resolve conflicts from upstream

Sort out all conflicts from upstream (tags), fix CSS issues in popup.
Update documentation

Update CHANGES and README.md file to better fit the Toggl Button for
Custom Websites extension.
Update manifest

Change name and description in manifest.json file to reflect branched
Toggl Button for Custom Websites extension.
Tweak wording

plugin > extension
Tweak text

Tweak text a bit for this customized branch.
Update README

Update disclaimer, Chrome Web Store link, and other text in the README
file.
Fix verbiage

branch > fork
Update README text

Update wording for usage steps, add extra line break.
Fix bug

Fix bug which requires user to view Settings page every time extension
restarts in order for custom websites to work. Also create
setCustomWebsitesCheckbox helper function.
Update CHANGES file

Update CHANGES file with release info for version 0.4.4.1.
Get updates from upstream

Get updates from version 0.4.5 from upstream.