Proof reading part of chapter 2

It also fixes wrong address of file darkroom_module_icon_picker.png
Proof reading of section 2.2 of the usermanual (file fr.po) of darktable 1.5

Substitution of french word vignette by miniature in the entire file fr.po
	modified:   ../doc/usermanual/po/fr.po
Minor update in the translation of the usermanual.

First use of Poedit.

	modified:   doc/usermanual/po/darktable-usermanual.pot
	modified:   doc/usermanual/po/fr.po
proof reading of darktable's usermanual till import images from camera

	modified:   ../doc/usermanual/po/fr.po