[UI] improve GGPK reading performance

[vlad-zhukov]

2 changes:

1. Add an optional callback function to GGPK reader that can be used for subscribing to the reading process instead of wrapping (mutating) internal functions.
2. Add a timer to only emit progress bar changes once every 200ms. This is a huge performance impovement.

[coveralls]

Coverage decreased (-0.006%) to 38.623% when pulling 2c83ff02b1d939f44e6406fb684138df721f2c5e on Vlad-Zhukov:dev into 0cde263b0a82e8ad073d03861671997e45bce857 on OmegaK2:dev.

[OmegaK2]

I feel like adding the callback function would actually make the original function slower (matters for the API reads), not that I mind limiting the speed at which the reader updates. If you can update with just the UI code I'll merge the changes, but otherwise I won't.