- added foundation for server-sent alerts (related #53)

right click & middle click now get triggered by keybinds (uses auxclick event)

- main canvas & blank canvas drawing moved to separate worker thread (if possible)
- server jobs moved to separate process (fixing CPU leak on heatmap generation)
- pixels now store if they are on top reducing db queries
- remove various methods to store pixel data in redis, reducing delay for various actions

additional fixed: (came up during performance fixes)
- added square fill (fixes #15)
- redraw loop (fixes #59)
- added keybind to deselect current color (fixes #54)
- pixel undos no longer delete the pixel from the db
- server logging now indicates what module triggered the log