Added new test for ELCompiler
Reimplemented EL parser using parser combinator
Added support for maps in ELCompiler
Added support for nested seq/maps access in ELCompiler
Added support for other collections in ELCompiler
Refactored ELCompiler. Resolves #1951
Merge pull request #1956 from excilys/el-parser

EL parser based on parser combination, close #1951