Stability: Throttle charm writing more aggressively and eventually pause it

[seefeldb]

We're already throttling writes from a charm, but we could throttle more aggressively if it stays active for say >10s and the window doesn't have focus. And then maybe after 30s or so just pause it and show a dialog?

[jsantell]

Similar to #739, but possibly distinct

[tonyespinoza1]

this charm might be useful as a reference point of a runaway train... about 174 emails... the charm runs... but take a look at the console... https://toolshed.saga-castor.ts.net/tonymail/baedreih7z3yjhjxzmju6ll4yd3dvktuvaj7unabnvgizhx3wpeqwkpmhca