V2.0

# Version 2.0 release
This version adds a lot of functionality, of which:

- [x] Under construction checkbox to indicate that your PR is still under active development and not ready to merge. (idea borrowed from Github dev team)
- [x] Better script initialisation. Scripts now only execute logic when the DOM is either in readyState `interactive` or `ready`.
- [x] Disables the merge button when using a git-flow branch. This helps a lot, because now your junior devs will not make this mistake. Branches created via git-flow should be finished via git-flow.
- [x] The template has gotten an upgrade. It now includes 'documents', a section where you can attach urls and attachments of documents that are of importance to the PR. In case you had a custom PR template, you can restore it by using the button in the options page.

## Special thanks
Special thanks this time goes out to the whole @SEOshop team for testing the extension in their development cycle. They have discovered some of the bugs covered in this version release.

## Why this is v2.0 and not v1.2
Because the template has been changed, it requires the user to change it himself.