Project manager: Sped up project load

[iLLiCiTiT]

Brief description

Speed of project loading was enhanced by ignoring signals during initial project item creation.

Description

Blocking of signals during that time cause that filtering and repaint of view is not triggered which makes everything much smoother. Also refresh button forces to refresh current project.

Testing notes:

1. Open project manager
2. Select project
3. Load of project entities should be 3x faster

[BigRoy]

Testing this here now - but it doesn't appear much faster on my end. The only side effect after this PR is that now it doesn't show the "Working..." overlay anymore and thus it feels like it's hanging more than before.

Correction. This PR is making it lightspeed compared to what it was before. Thank you very much!

[iLLiCiTiT]

The only side effect after this PR is that now it doesn't show the "Working..." overlay anymore and thus it feels like it's hanging more than before.

Project manager never had that overlay?

[BigRoy]

This PR has introduced a bug where the Tools column doesn't show the correct data visually until when double clicked and editable.

After

What I'm seeing on refresh (note the empty line compared to the next screenshot):

When double clicking the tools for a specific asset

Before

---

Note also how the table view doesn't show all the editable columns. I have a hunch that maybe delegates aren't being registered correctly?