Consolidate backlog fetching / review backlog fetching

[samueldr]

This part is now a mess technical debt alert! because there are two bits that may concurrently load the backlog. This isn't an issue in itself, but it should still strive to be representative of good coding skills.

Backlog fetching should be queued in an array or an object to document the intent of making a backlog fetch. This will stop double fetches.

Furthermore, backlog fetching should be able to handle "until line" option, which will help a partial live log be filled as needed.

Backlogs fetching should also always be truncated until the first line in the live log (by line number), right now, if a backlog fetch fetches lines 1-122 and the queue sent line 121, the backlog fetching via API will repeat line 121 and 122. (Not that big of a deal though)

[samueldr]

Well, it's becoming an issue...