SDK: Shielded-Sync should broadcast events

[jurevans]

When shielded sync starts, we should transmit progress events (ProgressBar) that contains:

• current
• total

More info TBD

[euharrison]

Currently, the loading skeleton will be displayed to user while we are shield syncing

This is expected as it could take a huge amount of time (several minutes) depending on how many blocks the interface need to syncs

When we have the progress events transmitted, we can improve the interface adding a progress bar.

It's important to notice that it'll not going to have impact in the time consumed to sync, it's only a user friendly feedback while this is syncing