WIP: refactor Systemcall

WIP: refactor Systemcall

**WARNING; only compilation has been ested; even that does not work**

The goal of this commit is to use the list-based API to
QProcess::start, to avoid annoying syntax issues (see issues with
pasting from LaTeX).

* Create a new latexEnvironment() in filetools.h that returns a
  map<string, string> containing the variables and their values.

* Rewrite parsecmd() so that it returns a QStringList of tokenized parameters.

* Use this in startProcess. This is the part is is not finished yet.

Obviously, this will not be possible to get right for 2.4.0.