On-Off Switch for building the openfluid-landr library

* Added OPENFLUID_ENABLE_LANDR variable in CMake configuration
  to switch on or switch off the build of the openfluid-landr library
  
(closes #32)
Reintegrate basic accessors to GeovectorValue

* GeoValue and children are now only opened in read-only mode
Adaptation of the FindOpenFLUID module for CMake

* Updated default list searched OpenFLUID components, taking
  into account available components
* Fixed CMake configuration for enabled/disabled libraries
* Added FindOpenFLUID test

(references #36)
Merge branch 'develop' of https://github.com/OpenFLUID/openfluid into refactor-geovalues-2
Add of GEOS definition helper in OpenFLUID helpers
Removal of deprecated ScalarValue type
Add of observers paths in openfluid-minimal application

(closes #86)