up #443
 - add support for complex numbers in slepc
up #460:
 - use map of expression in order to handle expressions
fix #482
 - add support for map of ginac expressions
 - this is used to in #460 for boundary conditions
Merge branch 'feature/operator' of https://github.com/feelpp/feelpp into feature/operator

Conflicts:
	feel/feelpde/operatorpcd.hpp
	feel/feelpde/preconditionerbtpcd.hpp
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