Add option for disabling rtags autostart

[Armoken]

Hi. When I use cquery, cmake-ide still starts rdm daemon, which is useless, but it starts indexing of current project and create useless messages and buffers.
Is it possible to implement options for disable rtags autostart, because some cmake-ide features are convenient in joint use with a cquery.

[atilaneves]

It's possible, but I don't know why you'd not want rdm to start if you have it installed. PRs welcome.

[rileyrg]

rdm should probably be installed as systemd service. And thats how its documented in most decent wikis.