[BUG]: ZHTLC sync progress

[smk762]

ref: KomodoPlatform/komodo-defi-framework#1922

This introduces 3 new options for sync:

• earliest, which begins at the sapling_activation_height in coins file
• date, which begins at a unix timestamp
• height which begins at a block height.

If these are not defined, sync will being approx 2 days in the past.

Previously, sync began at the checkpoint block in the coins file (1900000). The current progress percentage assumes this as a start point, so if set earlier it can look a bit wierd.

For the 0.6.1 release, the checkpoint block height will be used as the height sync param value to retain effectively the same flow as before.

In future, we can add a form so user can select an earlier block / date and still have a sane sync progress display.