Add helper script for creating new type versions

[magnusbaeck]

Description

Adding new versions of events (or other types) is rather painful, at least if you want to do it for multiple types; you need to locate the latest event version, bump the appropriate digit, copy the hitherto latest version to a new file (and after #341 has been implemented, update the new file with the new version). We should write a simple script that does this chore for select types and choice of magnitude for the update (major/minor/patch). It should also add an entry to the history table.

Motivation

This will make it much less tedious to make bulk updates of types.

Exemplification

To create a new minor version of all activity events the command could look like this:

./bump_version.py minor EiffelActivity*Event

Benefits

Obvious.

Possible Drawbacks

None.