Ability to control static build of plugins separately.
MagnumPlugins: no need to install testing libs, as they are all static.
TextureTools: shorter filenames for headers.

To be consistent with the rest, I don't know how did I forget about
this. Also it seems that the resource import header was never used, as
it included long-gone magnumConfigure.h. Thus I'm also not maintaining
any backwards compatibility, because it never worked in the first place.
Require at least CMake 2.8.9.
Use POSITION_INDEPENDENT_CODE CMake property.

New in 2.8.9, much cleaner than the previous "solution". Also cleaned up
the surroundings a bit. Fixed cases where PIC was forced independently
of the settings, for plugins the PIC is now also set only when
needed/requested.
No need to install static test libraries on Windows.
Platform: print all CORRADE_TARGET_* flags in magnum-info.