Fixes
- Tell ace about Function node globals. Closes #927
- Tidy up mqtt nodes - linting and done handling. Closes #935
- Fix invalid html in TCP and HTML node edit templates
- Add proper help text to link nodes
- Handle importing old mqtt-broker configs that lack properties
- Update ace to 1.2.4
- Allow config nodes to provide a sort function for their select list
- Add log warning if node module required version cannot be satisfied
- Handle empty credentials file. Closes #937
- Add RPi.GPIO lib test for ArchLinux