TEXTE_MODULE cleanup in preparation for text on different layers
- Removed the friends MODULE and FOOTPRINT_EDIT_FRAME from TEXTE_MODULE
  (as in the @todo comment)

- Refactored the Rotate/Flip/Mirror for text in modules into the
  TEXTE_MODULE class itself (members RotateWithModule, FlipWithModule,
  MirrorWithModule)

- New behaviour in coloring text on screen: reference and value still
  take the color from the MOD_TEXT_FR_VISIBLE and MOD_TEXT_BK_VISIBLE
  visibles; other text takes the color of the layer containing it
  (except when hidden, obviously) but still get its visibility
  controlled by those visibles (probably the most intuitive and useful
  behaviour)

- Still need to decide: should text on a layer be hidden when the layer
  is? Probably yes (still to be implemented);

- Some comment fixed and many cast converted to static_cast
More work on module texts, and especially on the collector 

The members SetIgnoreMTextsOnCopper, SetIgnoreMTextsOnCmp,
SetIgnoreModulesOnCu, SetIgnoreModulesOnCmp in the collector guide are
renamed to the clearer SetIgnoreMTextsOnBack, SetIgnoreMTextsOnFront,
SetIgnoreModulesOnBack, SetIgnoreModulesOnFront

Modified the collector and drawing behaviour for text in modules as
discussed in the mailing list.

* Now module text on layers different than Silk should work! *

Still need UI support for setting the layer in the module editor.
Overhaul of footprint wizard helpers
WIP: Inline headers
WIP: Lemo sockets