Introduce a PlatformStyle to handle platform-specific customization of
the UI.
This replaces 'scicon', as well as #ifdefs to determine whether to place
icons on buttons.
The selected PlatformStyle defaults to the platform that the application
was compiled on, but can be overridden from the command line with
`-uiplatform=<x>`.
Also fixes the warning from #6328.
QT_NO_KEYWORDS prevents Qt from defining the `foreach`, `signals`,
`slots` and `emit` macros.
Avoid overlap between Qt macros and boost - for example #undef hackiness
in #6421.
The wallet now uses the mempool fee estimator with a new
command-line option: -txconfirmtarget (default: 1) instead
of using hard-coded fees or priorities.
A new bitcoind that hasn't seen enough transactions to estimate
will fall back to the old hard-coded minimum priority or
transaction fee.
-paytxfee option overrides -txconfirmtarget.
Relaying and mining code isn't changed.
For Qt, the coin control dialog now uses priority estimates to
label transaction priority (instead of hard-coded constants);
unspent outputs were consistently labeled with a much higher
priority than is justified by the free transactions actually
being accepted into blocks.
I did not implement any GUI for setting -txconfirmtarget; I would
suggest getting rid of the "Pay transaction fee" GUI and replace
it with either "target number of confirmations" or maybe
a "faster confirmation <--> lower fee" slider or select box.
- add missing license headers
- make compatible with Qt5
- enforce header cleanup style
- small code style cleanups
- rename Coin Control dialog into Coin Control Address Selection
- use default font for the windows labels (no monospace)
