Replace SW_HOME/shell with SW_COMMON_SHELL_HOME
Bugfix: Disable caching for 2 weeks

Currently the updater will not work properly because it has been cached by our
users, but had a bug where, when the update occurs, it does not properly delete
the cache file.  Therefore, the cache will never be updated, therefore the
updater will never be updated.

The only way to circumvent this is to set `export SW_CACHE="false"` in the
bootstrap file.  This file is never cached and therefore will be read fresh on
every shell load.

Once this is read, along with the next line to clear the cache file, the correct
updater will be read from disk.

This will take 7 days to propagate through all shellwreck users, at which point
this can be removed.
Refactor: Rename shellwreck_update_check to _sw_update_check
Refactor: Rename eligible_for_update_check
Refactor: Add _sw_auto_update_enabled
Feature: Don't check for updates at all if auto updates are disabled

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Branch:        feature/fix-updater-for-cached-usage
Signed-off-by: Jeff Felchner <accounts+git@thekompanee.com>
Refactor: Rename shellwreck_update to sw_update
Refactor: Move _sw_update_check into the plugin file
Feature: After checking for an update, return to previous dir
Feature: Always load the updater from disk even if cache is enabled
Bugfix: Make sure to reset before update so there are no checkout errors
Merge branch 'feature/fix-updater-for-cached-usage'