fix pasting/attaching with unicode chars (#813, #867)

- treat # specially instead of quoting entire string, as urllib unfortunately
  can't handle utf8 quoted text
- make sure we pass utf8 to quote() in _addMedia()
handle % as well (#823)
replacement order must be reversed
ensure we match on identical closing quote (#769)
force webkit to output <br> when enter pressed, instead of div

this should make it easier for mobile clients to convert into newlines
canonify tags when saving, and strip quotes (#794)
separate messages for 50x errors
support unc pathnames again

Turns out that WebKit does support UNC pathnames in the base tag, but it is
picky about the leading number of slashes.
better warning when apkg invalid
shortcut to jump to tags entry
print to console when existing copy running
disable dragging of images in review window (#420)

webkit's default behaviour is to remove them from the media folder otherwise,
which we don't want
remove pyqtconfig usage (#831)
add a 'safe mode' (#797)
cloze deletion tweaks (#601)

- allow creation of cloze deletion when note type not selected; warn with
tooltip. prevents selection from getting lost
- warn before adding cloze note type with no deletions
convert about to webview so we can scroll if too small
need greedy match on images
leave new cards alone when exporting, so order is preserved (#447)
ensure fmax>=fmin when rescheduling