* Replace instances of 'KeePassX Reboot' with 'KeePassXC'
* Lowercase headers to be consistent with README
* Add more headers to the table of contents
* Make the link to the issue tracker more prominent (preferred over
Google Groups, apparently)
* Add information about the #keepassxc-dev IRC channel on Freenode
* Add 'hotfix' to the branch strategy (seems in the standard and
is also used)
* Rephrase some paragraphs to make them clearer, fix a few typos
* Ask user to remove lines that don't apply instead of changing emoji
* Replace KeePassXR with KeePassXC
* Add help text how to find KeePassXC version [skip ci]
* Combine documentation requirements into one [skip ci]
* DOC: Add ISSUE and PR template, add CONTRIBUTING
* DOC: incorporated feedback from @samrocketman, @Manko10, and @droidmonkey
* README now points to CONTRIBUTING instead of repeating it
* Added code style link and minor tweaks to CONTRIBUTING
