transmission: Update to 2.77.

Minor update to the latest stable version.

A lot of more changes:
* Splitt into subpackages - transmission, transmission-cli and transmission-daemon.
* Create transmission user and group for daemon.
* Add systemd file and scriptlet for daemon.
libnfsidmap: Set pluginpath.

Set the pluginpath for libnfsidmap to be able to dynamically load and find the required plugins.
Merge remote-tracking branch 'stevee/libnfsidmap-fix'
Merge remote-tracking branch 'stevee/transmission-update'