Location Switcher - Advanced wót Ethan Liu

This add-on was based on “Location Switcher” with more powerful features and needs more permissions.

Differences from original version:
- Option for replacing the favicon

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Location Switcher lets you switching between sites by click the ☯ icon from the address bar.
In most cases, you would like to switch between development and production sites.

For example a simple route:

http://localhost <-> http://remote.example.com

Multiple destination for the same source:

http://dev.local <-> https://production.server
http://dev.local <-> http://test1.stage.server
http://dev.local <-> http://test2.stage.server

Custom routes: (Loop option unchecked)

http://dev1.server -> http://dev2.server
http://dev2.server -> http://dev3.server
http://dev3.server -> http://dev1.server

## Source code

https://github.com/ethanliu/location-switcher-addon