Add write mesh method - should be finished, add basic write_data method
Add write mesh method - should be finished, add basic write_data method

Still need to specify interpolation matrices and refine data writing for
more general cases.

vlukes/sfepy,BubuLK/sfepy,BubuLK/sfepy,sfepy/sfepy,vlukes/sfepy,sfepy/sfepy,BubuLK/sfepy,sfepy/sfepy,rc/sfepy,vlukes/sfepy,rc/sfepy,rc/sfepy