Change "Default repository" connected to room

Created by: dregad

Currently, when someone references an issue (i.e. #nnn) in an org room, the ID is highlighted, but the link is not valid, as shown in the screenshot below (example from https://gitter.im/ADOdb?at=559d2c0621e1d6761f2a3113):

I would suggest to add a setting for organization room, to set a Default Repository, which would allow Gitter to build functional links.

e.g. in org room XXX with default repository RRR, we could use any of the following references

• #nnn: issue in default repository, transformed to XXX/RRR#nnn
• SSS#nnn: specific repository, transformed to XXX/SSS#nnn
• XXX/RRR#nnn: fully qualified link, no transformation needed

Until then, I believe Gitter should not turn an issue reference into a link if the target does not exist.