Fix #2149 - Part 1 - Add configuration setting for explorer refresh

[bryphe]

Issue: There can be a performance degradation when upgrading from Oni 0.3.2 -> Oni 0.3.3 due to the way we watch the file system / update the UI in response to it.

Fix: We'll gate the 'autoRefresh' behavior behind a flag - explorer.autoRefresh, which defaults to false. We'll enable an explicit refresh gesture with the explorer.refresh command, bound to <C-r>.

[bryphe]

Note that this doesn't completely address #2149 - we should also hook up the oni.exclude files configuration to work with the explorer file watching (and investigate other ways to optimize the perf as @Akin909 mentioned).

[codecov]

Codecov Report

Merging #2154 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #2154      +/-   ##
==========================================
- Coverage   37.04%   37.04%   -0.01%     
==========================================
  Files         293      293              
  Lines       11979    11980       +1     
  Branches     1582     1582              
==========================================
  Hits         4438     4438              
- Misses       7289     7290       +1     
  Partials      252      252

Impacted Files	Coverage Δ
browser/src/App.ts	6.75% <0%> (ø)	⬆️
browser/src/Input/KeyBindings.ts	2.22% <0%> (-0.03%)	⬇️

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