Replace selected text when using paste dialog

Fixes issue 4162

Change-Id: I0d4997c8ced84efbc1ed31276b48133ffcce909a
Reviewed-on: http://gerrit.dmdirc.com/1261
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>

Change-Id: I13bd658b58560fbd383320a7a2aaa7c831429490
Reviewed-on: http://gerrit.dmdirc.com/760
Automatic-Compile: Chris Smith <chris@dmdirc.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>

Change-Id: I398028d98b2bd1902ee8ec26d58f21a4ad87436a
Reviewed-on: http://gerrit.dmdirc.com/757
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>