Fix clean-all target and robust link creation.

Move creation of links from source tree to build tree to CMake lists.
Add CMake target clean-links.
Automatically collect all links and delte tehm by this target.
Fix wrong directory name for GTest build subdirectory.
Clean unnecessary targets in main makefile.
Small changes in README to follow current Petsc
Merge branch 'master' of github.com:flow123d/flow123d
Small changes in README.md
Can set root build directory by BUILD_SPACE var.

Necessary for Jenkins builds.
Merge branch 'master' of github.com:flow123d/flow123d
Add include necessary for new boost.

... in particular boost/program_options
Changes to satisfy g++ 4.4
Added embeded icon with build status to display at GitHub
Merge branch 'master' of github.com:flow123d/flow123d
Small changes in README.md
Consistent headers in README.md
Test commit to trigger post commit hook
Another stupid commi to trigger build of master at CI server
Test commit
Try to fix running unit tests
Improve code documentation.

no code change
Merge branch 'master' of github.com:flow123d/flow123d
Reorganization of mass balance.
- New class MassBalance separated from the transport equation.
- Balance is calculated at each computational time step, not only at output times.
- Units added to text output.
- Updated reference manual with description of calculated quantities.
- Files mass_balance.txt added to reference results of all relevant tests.

TODO:
- Explicit transport still produces significant error in cumulative bilance, especially at times when boundary condition changes.
- Calculation of mass balance may slow down the explicit transport (to be checked). Possibly implement option to switch off mass balance.
- Balance does not work with reactions.
Optimization of Input::Address class