Fix of resizing problems in Builder due to very long dispalyed string

* Added ElidedLabel class based on QLabel
* Replaced QLabel widgets displaying long strings
  by ElideLabel widgets  

(closes OpenFLUID/openfluid#368)
Fix displayed paths in Builder with correct path separator

(references OpenFLUID/openfluid#420)
Escape of XML special chars in parameters when saving to fluidx files

* Added specific function in openfluid::tools for
  escaping special XML entities
* Updated tests

(closes OpenFLUID/openfluid#418)
Update of CHANGELOG and switch to version 2.0.1~beta2