Extract tab lifecycle events

[sammacbeth]

Reviewer: @kzar

Description:

• Currently, events that trigger updates to the data in tabManger global are strewn about several parts of the codebase.
• This PR moves all these events into a single 'component', which is initialized on startup. This keeps all this code together in a single, short(ish) initialization function.
• This also updates tabManager initialization, to load existing tabs ASAP (it was previously delayed behind several async startup processes), which should limit startup race-conditions.
• This refactor will also help us make this code compatible with Safari in the feature, where the unsupported events here will have to be replaced.

[jonathanKingston]

I think this is fine, just going to leave it out the latest build to reduce risk as people are away etc.

[jonathanKingston]

Cheers for the changes :)