refactor ResourceIdentifier.resource_id (to be able to use decorators)
refactor ResourceIdentifier.resource_id to ResourceIdentifier.text,
deprecate old property
refactor ResourceIdentifier

Keep attributes text/prefix/uuid separate and decide via self.fixed how
the current text representation looks like.
For fixed case: return user set text
For non-fixed case: return prefix + current uuid hash

Also introduces the possibility to regenerate the hash part for
non-fixed resource identifiers (useful for the referred object to get a
new hash when the referred object changes)
Merge branch 'master' into resource_id_refactor

Conflicts:
	obspy/core/event.py
some more refactoring for resource identifier
Merge remote-tracking branch 'upstream/master' into resource_id_refactor

Conflicts:
	obspy/core/event.py
change from resource_id.text to resource_id.id
Merge remote-tracking branch 'upstream/master' into resource_id_refactor
correct one missed replacement in 5d2979774ece, correct a tested warning
changelog for changes to ResourceIdentifier
Merge pull request #673 from megies/resource_id_refactor

ResourceIdentifier refactoring