Fixed VisualStudio hang during deployment of .bar file

As the MSBuild task was capturing all for itself.
Improved 'make clean' call

That makefile call will receive QNX_HOST, QNX_TARGET variables along with MAKEFLAGS.
Helping in loading more complex makefiles (like the one from Cascades project).

Additionally makefile can be optionally placed next to the project file.
Fixed BBNativePackager to skip empty assets

BBNativePackager was failing on creation of valid set of ITaskItems for embedded assets,
when empty 'value' was specified for given 'path'. Also it was looking for
them via $(SolutionDir), what is now changed to $(ProjectDir).
Extended MSBuild to pass makefile's target name

Since this commit it is possible to compile and deploy Cascades applications.
The only limitation is that developer must set 'Custom Makefile' and
'Device-Debug' makefile target in project settings and manually maintain
the makefile/.pri/.pro files (or copy them from Momentics).
Added full Cascades-App type of project support

It is now as easy as selecting 'Cascades Application' in project settings.
The makefile and .pro files must be copied from Momentics (or in the
future generated by new-project wizard) and .pri file is automatically
genrated to match the current project.