New Init method for AEAudioUnitFilter to allow for default format

Incorporated new init method with a useDefaultInputFormat argument, which specifies whether a filter should enforce conversion to its preferred input format. 

Solves an issue with units like the 3D mixer which, for example, requires a mono format but doesn't throw an error if a different format is set on the unit. 

(Reverted my earlier commits to my fork which would have caused conversions to happen more often than would be desired.)