[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.
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
Move only: extract WriteChainState and UpdatedTip from SetBestChain.
Prepare block connection logic for headers-first.

This changes the block processing logic from "try to atomically switch
to a new block" to a continuous "(dis)connect a block, aiming for the
assumed best chain".

This means the smallest atomic operations on the chainstate become
individual block connections or disconnections, instead of entire
reorganizations. It may mean that we try to reorganize to one block,
fail, and rereorganize again to the old block. This is slower, but
doesn't require unbounded RAM.

It also means that a ConnectBlock which fails may be no longer called
from the ProcessBlock which knows which node sent it. To deal with that,
a mapBlockSource is kept, and invalid blocks cause asynchronous "reject"
messages and banning (if necessary).
Per-peer block download tracking and stalled download detection.

Keep track of which block is being requested (and to be requested) from
each peer, and limit the number of blocks in-flight per peer. In addition,
detect stalled downloads, and disconnect if they persist for too long.

This means blocks are never requested twice, and should eliminate duplicate
downloads during synchronization.
Limit the number of orphan blocks

In case the total number of orphan blocks in memory exceeds a limit
(currently set to 750), a random orphan block (which is not
depended on by another orphan block) is dropped. This means it will
need to be downloaded again, but it won't consume memory until then.