doc: starts manual in doc folder

adds manual.tex including preliminary table of contents
Merge branch 'master' into manual
doc: adds content to GUI quick tour of manual
doc: fixes typo in manual
Merge branch 'master' into manual
doc: finishes GUI part of the quick tour in the manual

replaces doc/manual/fig/gui_imagevis_gradient.png due to change in
Gradient worker (#96).
doc: adds content to scripting part of the quick tour in the manual
doc: finishes the quick tour section in the manual
implements #99: minimal version of user manual

the manual is located in doc/manual
Merge pull request #100 from aheld84/manual

Minimal version of manual