Allow users to set the trigger height for lengthy toot auto-collapse (#2070)

* Allow users to set the trigger height for lengthy toot autocollapse

Add a field in the glitch-soc preferences to set the exact height in pixels of a "lengthy toot" where auto-collapse is triggered

Originally authored by Dean Bassett (github.com/deanveloper)

Squashed 3 commits from neatchee/mastodon and returned some values to project defaults:
* ef665c1df5821e684c8da3392049f33243fafa74
* 0fce108d210efe55027a3af061bfc57aaaa83843
* 998f701a2b2e37edbda7dffb11a61f67f5559b18

* Remove bad escape characters

* Apply feedback from glitch-soc code review
- move input width specification to CSS
- adjust language for clarity

* Update comments re: lengthy toot height

* Fix inconsistent indentation

* Use a calculated width that scales better with browser font instead of static 45px width

app/javascript/flavours/glitch/reducers/local_settings.js

@@ -37,6 +37,7 @@ const initialState = ImmutableMap({
       reblogs          : false,
       replies          : false,
       media            : false,
+      height           : 400,
     }),
     backgrounds : ImmutableMap({
       user_backgrounds : false,