Less roundtrips through to the UI on changes for better performance/UX
Also adds "flash" protection to deal with the active editor changing to undefined between changes

This setting allows disabling/enabling showing avatars in hovers. We
already have settings for the explorer and blame gutter, so it makes
sense to also have one for the hovers.

Closes #419 - Make blame heatmap color configurable

- add "-c color.branch=never" option to git branch commands, definitively disabling color branch output

.# Discussion

Branch names are mis-parsed if `git branch` output is colored (eg, when git is configured
with "config.branch=always"). Using the base "-c color.branch=never" option overrides any
user configuration, displaying git branch output as uncolored in all cases and fixing the
issue.

Notably, option ordering is important in this instance. The "-c ..." option is a git
base option, not a git branch subcommand option. So, as done here, it must be inserted
before the "branch" subcommand.

ref: Issue #415