Install parser headers and cmake config files to support client packages

Summary:
Generated headers, which may be required by client packages, are installed
into a private and version specific include dir to indicate that they may
not be stable.

To use the parser in client packages simply add kdevphpparser with
target_link_libraries to a target. Parser related headers need to be
prefixed with <parser/...> e.g. #include <parser/tokenstream.h>.

BUG: 388370

Test Plan: compiled on linux, verified with patched umbrello build

Reviewers: pprkut!, kfunk, mtijink

Subscribers: brauch, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D9624