[Enhancement] Adds ability to enable/disable sources

[kieraneglin]

What's new?

• Adds the ability to enable/disable a source. Disabling kills all download/indexing tasks and enabling re-starts those tasks as needed
  • You can still manually run an index or download even if a source is disabled
  • Resolves [FR] Disable sources or profiles #412
• The kickoff of a slow indexing task now takes the time of last index into account. In other words, indexing will wait until the appropriate time if you change your indexing settings back-to-back-to-back on a source that was recently indexed
• [Unrelated] Added source count to the media profile index page
• [Unrelated] Added links to the relevant tabs for the numbers on the media profile/source index pages

What's changed?

N/A

What's fixed?

N/A

Any other comments?

N/A