Add "Revealer" seed backup plugin (#4228)

* revealer commit

* fix seed font, added license

* fixed strings for translation

* better calibration instructions, fixed position

* removed html from translatable strings, fixed typo

* Added monospace font for codes, cleaned up redundant font formatting

* Monospace font for codes and respective license

* fix redundancies, typos

* inner function to only move forward if no exception

* paint QR qith QT to not depend on PIL
catch exeptions when creating a digital Revealer

* clarity

* Added SourceSans font License

* fix fonts paths, typo

* broke long lines, changed some words for clarity,
removed redundant font license

gui/qt/seed_dialog.py

@@ -26,6 +26,8 @@
 from electrum.i18n import _
 from electrum.mnemonic import Mnemonic
 import electrum.old_mnemonic
+from electrum.plugins import run_hook
+
 
 from .util import *
 from .qrtextedit import ShowQRTextEdit, ScanQRTextEdit
@@ -194,4 +196,5 @@ class SeedDialog(WindowModalDialog):
         title =  _("Your wallet generation seed is:")
         slayout = SeedLayout(title=title, seed=seed, msg=True, passphrase=passphrase)
         vbox.addLayout(slayout)
+        run_hook('set_seed', seed, slayout.seed_e)
         vbox.addLayout(Buttons(CloseButton(self)))