[Qt] add messages when handling local payment request files

- important for the open URI dialog to give users feedback
  when a file is invalid etc.
Store orphan blocks in serialized form
Tweak linearize.py to give more flexibility

Add the ability to start at a non-zero height, and allow for appending to
an existing file.
Merge pull request #3518 from Michagogo/linearize-start-value

Tweak linearize.py to give more flexibility
build: fix MacOSX build after ec41342

Fix regression introduced in ec41342.

Also use a less ugly solution, by defining the value of
`MOC_DEFS` in the configure script instead of `Makefile.include`.
Merge pull request #3524

67d60f7 build: fix MacOSX build after ec41342 (Wladimir J. van der Laan)
qt: Minor message updates

Used sending/receiving addresses -> Sending/receiving addresses
Previously requested payments -> Requested payments (idea from @cozz in #3521)
Merge pull request #3374

bd70562 [Qt] add messages when handling local payment request files (Philip Kaufmann)
Merge pull request #3528

66a8829 qt: Minor message updates (Wladimir J. van der Laan)
qt: English translation update
Merge pull request #3532

f087ce8 qt: English translation update (Wladimir J. van der Laan)
Merge pull request #3516 from sipa/serorphans-head

Store orphan blocks in serialized form
wallet: add interface for storing generic data on destinations
[Qt] Permanently store requested payments in wallet