Not sure if it makes any difference, but won't hurt to add it in

Closes #667

* Add confirmation dialog for Remove All

* Show Remove All confirmation dialog only when clicking the action

* Add confirmation dialog for New File as well

* Simplify slot_fileNew

* Tweak return indentation

* Remove slot_ prefix and decoration

* Create midi-channel-ab.c

midi-channel-filter.c + bits of midi-split.c = an attempt at a per channel output A/B routing

* Update Makefile for ab plugin

* Update midi-channel-ab.c

fixed incorrect copy/paste

* add A/B plugin

* Add A/B plugin

* Add A/B plugin

* Add A/B plugin

* Add A/B plugin

* Rename and reorder binary options

* Fix output order

* Fix order(?)

* Fix order

* More efficient code, floats to booleans, comparison fixes

* Revert mistake

* Fix midi output port numbers

* Fix maker name

* Add copyright header line

* Add confirmation dialog for quitting Carla

* Make exit confirmation dialog configurable

* Don't save confirmExit in the host object

* Don't set host.confirmExit in loadHostSettings either

* Modify .ui file using qt4 designer

* Change config ui back to original size

* Put check for exit prompt on multiple lines

* Convert (not ==) to (!=)

Triggered by 8b1fd1f537
Closes #655

Closes #640

Fixes #653

Fixes #635

Merge as much as possible stuff from second loop to first. Use second
only to set width and X for ports.

More folding
Clean some magic height changes. Bottom space now consists of
max(port_spacing, port_spacingT) + border width - trailing port_spacing.
Port types are traversed in loop, using array.