Multiple Fixes

[tlskinneriv]

• Storage key for data to valid Windows file path, migration on first run, resolves awnet_local_data_<mac_address> as file name can't copy in Windows #26
• Last Rain sensor now behaving correctly, was previously updating to "Unknown" when it had no data,
  resolves Last Rain unknown most of the time when it should be the last timestamp #28
• Keys for lightning data storage are converted to strings by the storage provider, perform
  conversions when data is accessed, resolves TypeError: unsupported operand type(s) for -: 'float' and 'str' #29

[madsci1016]

Well, glad i checked bug fixes before spending too much time on this. Thank you for creating and maintaining this library. I was using lightning strikes per hour to set my DIY powerwall into storm mode, but didn't see that it was broken in the local integration when i switched to local a few weeks ago when the cloud integration broke. Now i see you have to recreate this variable because it's not exposed by AW. Oi. Cheers mate!