OCV vs. SOC curve configuration improvements

[martinjaeger]

Previously, only a pre-selected OCV vs. SOC curve for different cells could be selected, but the curve was not exposed via ThingSet. For the custom cell, every value had to be configured manually.

With the new approach, the custom cell is removed and instead the actual cell configuration can be pre-set with default values for different cell types. These actual values are now also exposed via ThingSet and can be adjusted as well.

[martinjaeger]

Thanks for testing.

I've only tested writing using the Android app via Bluetooth (I'm about to finally publish it in the Play store...) and afterwards checked the values on the shell. Looks like I should have tested writing on the shell as well ;)

It makes sense to increase the buffer size. Will add a commit, probably on Monday.