Use nf-core git branches

The latest stable release should be on the main master branch. No additional changes should be pushed to master after each release.

The main development code should be kept in a branch called dev. The nf-core dev branch should be set as the default branch up until the first release.

For minor bugfixes a patch branch may be used and merged directly into master, leaving dev for continued development work.

The TEMPLATE branch should only contain vanilla nf-core template code. It is used for automated synchronisation of template updates.