Add Windows JACK support (LMMS#5716)

Add Windows JACK support
Also adds JACK as a submodule

Disable fluidsynth audio backends if possible

Closes LMMS#649
Partially reverts LMMS#3446

Fix the AppImages

Patch exprtk on Clang < 3.9

Fix export - double dialog windows on writing over existing file (LMM…

…S#3526)

* Fix export - double dialog windows on writing over existing file

* Case sensitivity

Merge pull request LMMS#3476 from zapashcanon/shellcheck

Add shellcheck to the build

Add licensing information

Update classic theme (LMMS#3424)

Add rawwaves to Windows installer

Closes LMMS#3227

Add rawwaves to Windows installer

Closes LMMS#3227