QTextEdit() will pin the CPU at 100% for seconds to minutes when
fed a large string to display - work around it by switching to
QPlainTextEdit().
Also strip HTML before showing the user - easier to read, and less
text to display. And turn off word wrap, as it makes it easier to skim,
and further reduces the work the widget needs to do.
https://forums.ankiweb.net/t/big-issue-where-anki-gets-slow-when-you-import-this-deck/7050
Disabled for now; when enabled it will allow faster collection
open and close in the normal case, while continuing to downgrade
when exporting or doing a full sync.
Also, when downgrading is disabled, the journal mode is no longer
changed back to delete.
We no longer need to worry about pysqlite implicitly beginning
transactions, and can be more explicit about beginning/ending
transactions
save() now also has a trx argument controlling whether a
transaction should be started / left open
