Proxy domain should not be hardcoded to "home." or "remote."

[Tiller]

In app.js, to detect whether or not the application should proxify the request to the remote openhab, it looks at the domain name, and check if it starts with "home." or "remote.".

That a bad practice imho. It should simply check the domain against the proxyHost set in the configuration. Or at the very least, keep the check with "home." and "remote.", but include a check with the configured proxyHost

(Also, it'd be great for proxyHost to be documented in the README.md)

[lsafelix75]

#326

[Tiller]

#330

Not the same issue, why referencing it here?