Fixes and added functionality

[kiekerjan]

First of all, I think I messed up and now have one giant diff instead of nice little changes. Sorry for that :( I started out with the code of solmoller, and encountered some issues (notably #43, #47 and #48). While fixing those, I added some other stuff that I found convenient (your mileage may vary ;) ) The content: the summary can be found in the commit log. The most important change I made was to use the daily table in the local sqlite database.

• It seemed like the daily database was not used at all. I now store the daily production, serial number and the max power of the day in the daily table. This happens at the end of the day and when the inverter loses connection. Yes, this might cause multiple daily entries.
• The inverter table is not filled when the database.log option is disabled. I therefore use the daily production from the daily table to determine the production for the last 365 days. This used to be taken from the inverter table. The usage of the daily table is not influenced by the database.log option. However, the daily table should be accessed only twice per day per inverter: once to read the serial numbers and daily production (for 365 day production) and once to store the daily values.
• The database.log option was placed such that the $inverters{$inverter}{"data"} structure was not filled when this option is off. Because this structure is used by the json web thingy (I think), the web page was no longer updated. This has been fixed.

[kiekerjan]

I tested most of this for the past 10 days and seems to be working fine. Only the error catching code in the send_packets sub is more recent, but it does what I intended it to do. In my situation, my serial to tcp converter shuts down when there is no more sun, so I could not test the behaviour around midnight. It should store a daily entry for each inverter a little before twelve and then reset the daily read status somewhat after 12.