Eval::switch(): bugfix + additional tests
Parser::parse_value(): accept ',' and '.' as chars for normal values
Types::pixels: '' is not a valid value
Stat: simplify code, add docu
Parser::parse_value: Bugfix, accept eval("")
Parser::parse_value(): Bugfix, eval statement starts with a string
Stat: Sanitize eval statements of illegal values
Type::pixels: be more strict about accepted values

number + optional unit, e.g. "2" or "3.5px"
Compiler::compile_properties: catch non-compilable values
Eval: improve exec eval functions at compile time

- do not switch into database, rather execute code in local context
Types: new type 'numeric'; use for font-size and shield-font-size