Display progress of rescan.
Add progress to initial display of latest block downloaded.
Update the list of threads to the current state.
Make mining fee policy match relay fee policy.

This resolves a case in which a mismatch could be used to bloat up the
mempool by sending transactions that pay enough fee to relay, but not
to be mined, with the default policies.
Add script test to prove that OP_0 evaluates as the empty vector, rather than [0].
qt: Make it possible again to specify -testnet in config file

Changes for the datadir chooser have made it impossible to specify
the network (testnet/regtest) in the configuration file for the GUI.

Reorganize the initialization sequence to make this possible again.

- Moves the "datadir" QSetting so that is no longer dependent on the
  network-specific application name (doing otherwise would create a
  chicken-and-egg problem).

- Re-initialize translations after choosing network. There may be a
  different language configured in network-specific settings
  (slim chance, but handle it for sanity).

Fixes point 1 of #3840.
Merge pull request #3696

c4656e0 Add progress to initial display of latest block downloaded. (R E Broadley)
75b8953 Display progress of rescan. (R E Broadley)
Merge branch 'match_relay_fee' of git://github.com/mikehearn/bitcoin
Merge pull request #3844

c52c4e5 qt: Make it possible again to specify -testnet in config file (Wladimir J. van der Laan)
Merge pull request #3808 from paveljanik/master

DOC: Update the list of threads to the current state.
Merge pull request #3841 from schildbach/script-tests-OP_0

Add script test to prove that OP_0 evaluates as the empty vector.