Consolidate error_db resources into a new area apps/message_db. This contains the dADL message source files for the whole of adl-tools, i.e. all apps. It also contains a new command line tool that can read and validate these files (very simple currently, cross language validation still to come) and if successful, generate an Eiffel source file called COMPILED_MESSAGE_DB. This is written to the apps/message_db/generated directory. This directory is added as a cluster to every .ecf needing localised messages.

Improvements are possible:
- instead of generating a huge hash table, generate constants for the message texts, named using the keys. This would require the main source texts to be changed in all apps to use these first class constants rather than string keys. The advantage is that we know at compilation time if all messages are going to work, since now message ids would be statically resolved.
- the old run-time message builder code has been retained in RUNTIME_MESSAGE_DB, in case we want that functionality. I think it could be ditched, and the classes could be further simplified.
- the new msgdbc cmd-line tool is fairly hard-wired right now, although there are some options available. Possibly it should be made more flexible, e.g. with class name definable.
Merge branch 'master' of https://github.com/openEHR/adl-tools