init: clean up the SectionParser interface and Parser class

Remove the dependency on Action and Service from what should be a
generic Parser class.

Make ActionParser, ImportParser, and ServiceParser take a pointer to
their associated classes instead of accessing them through a
singleton.

Misc fixes to SectionParser Interface:
1) Make SectionParser::ParseLineSection() non-const as it always should
have been.
2) Use Rvalue references where appropriate
3) Remove extra std::string& filename in SectionParser::EndFile()
4) Only have SectionParser::ParseSection() as pure virtual

Document SectionParser.

Make ImportParser report the filename and line number of failed imports.

Make ServiceParser report the filename and line number of duplicated services.

Test: Boot bullhead

Change-Id: I86568a5b375fb4f27f4cb235ed1e37635f01d630