Pass IdentityManager into commands that use it.

Change-Id: Ieb89624746da92690df22b0938384141f42de8dd
Reviewed-on: http://gerrit.dmdirc.com/2676
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager
Stop IdentityManager initialising itself.

Instead, have Main provide the instance which becomes the
singleton. This allows us to inject dependencies to it, and
construct it using dagger later, while keeping all of the
code that calls the static getIdentityManager() method working.

Change-Id: I4ceaa062c84509bed66824f39cca8e76d25d131c
Reviewed-on: http://gerrit.dmdirc.com/2677
Reviewed-by: Greg Holmes <greg@dmdirc.com>
Automatic-Compile: DMDirc Build Manager