Expose Carla parameters for automation (LMMS#5846)

A new button called "Params" is added to the Carla instrument window; on press
it will open a new sub-window where Carla parameters can be found, ready for
connecting to a automation-track or controller. The exposed parameters in the
sub-window can be filtered by text and there is the ability to display only
parameters that are connected to a automation-track or controller. When there
are multiple plugins loaded inside Carla, the combo-box inside the (LMMS)
parameters sub-window can be used to switch between parameters of a specific
plugin (Carla).

Notes:

 - Available when compiled with Carla version 2.1 and up.
 - Currently Carla (2.1) will expose a maximum of 110 parameters.
 - The param window state isn't stored yet in a LMMS project, this is still
   TODO.
 - Connected paramters will NOT instantly disappear when they are disconnected
   with the "Show only knobs with a connection" filter enabled. See
   LMMS#5846 (comment)