Log warnings when bootstrap files are specified but cannot be opened

- Log a warning when bootstrap files are specified using `-loadblock`
but cannot be opened.
- Log a warning when bootstrap.dat exists in the home directory
but cannot be opened.
linearize.py: Harmonize rpcpass to rpcpassword

linearize.py: harmonize rpcpass to rpcpassword according settings in
bitcoin.conf
fix non-standard reason string in main.cpp
[Qt] allow translation of client bitness
Merge pull request #3649

3078b58 linearize.py: Harmonize rpcpass to rpcpassword (Subo1978)
Merge pull request #3643

d54e819 Log warnings when bootstrap files are specified but cannot be opened (Wladimir J. van der Laan)
Merge pull request #3614

b920148 [Qt] Improve single step in bitcoinamountfield (Cozz Lovan)
Merge pull request #3666

bbfce8a fix non-standard reason string in main.cpp (Philip Kaufmann)
Merge pull request #3587

ceb8e22 [Qt] allow translation of client bitness (Philip Kaufmann)
Let -zapwallettxes recover transaction meta data