Move code to set longitude/latitude into a function.

This is a code refactoring to be used by the undo support.
Add generic undo support in darktable.
Clear undo list when switching views.
Add undo for image position (geo-tag) in map view.

This used the new undo generic support.
Add support for redo.
Prefix all routines with dt_undo_ to avoid polluting namespace.
handle missing styles or not inited var in config file

  if the lighttable/export/style is not inited, or the style has been
  deleted, we default again to "none", to avoid using an empty string later
Verbose rawspeed exceptions
Let rawspeed identify itself in printfs
imageio_rawspeed: gotta catch em all
usermanual: a truckload of smaller changes - mostly language related
Merge branch 'master' of ssh://github.com/darktable-org/darktable
wb_presets: Pentax K-5 II s (thanks to Jack Bowling)
usermanual: another round of small fixes
The undo support is now based on a dt_undo_t struct on darktable object.

With this new desing it will be easier to have separate undo list for
different views if needed.

Change map view to use this new design.
Add mutex for the undo module.
thumbnails: avoid upsampling small embedded thumbs
noise profile: canon 650d by anton katsarov
wb_presets: Panasonic DMC-G5 (thanks to thouks)
usermanual: a bit of appraisal for denoisprofiled in feature list and basic workflow