Allow analysis start/stop and visualisation of analysis progress

**Description**
VG analysis frequently errors out when developing/editing an analysis workflow as it will be loading nodes while I'm moving nodes around or setting node filters. Can be frustratingly slow when trying to set up as you can't change the filters until the node has loaded, but you know you don't want see that data anyway. Would be ideal if you could add a bunch of nodes and/or set the filters then press something to start analysis.

Would also be great to be able to see the status of an analysis & cancel an analysis - I know I've caused lots of problems by kicking of multiple analyses at once then trying to delete a bunch (for valid reasons, and often bca I don't think anything is happening).

e.g. this happens to me most times I'm developing an analysis - once I'm done setting it up I always force re-load (either because I have to, or just to make sure that it's loaded correctly).

**Additional context**
Think this is a fairly widespread issue for anyone who is not using a template.