Lnbits

General fixes/improvements, mainly restoring the fee reserve improvements made to the Quart branch.

- Fixes issue of LNDHub extension linked to busy wallet taking down LNbits
- Support for AES-encrypted macaroons (for LND)
- Fixes LNURLwithdraw bug where withdraws would fail
- .env theme selection working properly
- Adds "bitcoin" theme

Updated LNURLPoS to LNURLDevices, to give the extension greater scope
Added admin users to allow easy debiting of admin accounts, and admin only extensions
Added FakeWallet, so LNbits can be used completely detached from bitcoin as a centralised payment server (for use as voucher system in schools, universities, businesses, events, etc)