just added the files with the parts of the buttons for the planner.

these parts must be put together, they were saved in parts to make it easy
for hover effects, etc.

Signed-off-by: Luisa Domingues <luisapiresdesign@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Mapped files of the planner icons on the subsurface.qrc file

[Dirk Hohndel: fixed several typos and changed the alias of the planner
               related plus / minus icons to avoid duplicate aliases]

Signed-off-by: Luisa Domingues <luisapiresdesign@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>