pidgin/pidgin

Change PurpleMessage:id to a string and add author-name-color to the property getter/setter.

This is in conflict with the TalkatuMessage:id property which will be addressed in another review request but Pidgin seems to run fine right now with this conflict.

Testing Done:
Compiled and ran locally against the history-api branch.

Reviewed at https://reviews.imfreedom.org/r/876/
---
name: libpurple-common
buildsystem: simple
build-commands:
- true
modules:
- external/avahi.yml
- external/cyrus-sasl2.yml
- external/farstream.yml
- external/libgadu.yml
- external/libidn.yml
- external/mercurial.yml
- gplugin.yml