add local time gatt characteristic

[cybuzuma]

Motivation

InfiniTime gains the Local Time GATT Characteristic in this PR. This characteristic sends information about the current timezone to the watch and thus allows it to calculate the current UTC.

Changes

• added a function that builds the bytes object for the characteristic. As I do not know of any "standard" way to get information whether DST is in effect in python, the code just always sends the information as DST = 0 (no dst).
• added code to send local time information if the corresponding characteristic is discovered on the watch
• corrected the Current Time data to use explicit little endian encoding

[theironrobin]

@cybuzuma do you still want this pulled in? i'm a bit out of the loop on this

[cybuzuma]

I still do.

While the feature is not yet merged in InfiniTime, I am confident it will at some point.
Having as many companion apps as possible support this would be great for users, especially as siglo is listed as the recommended application on linux, it would be great if siglo supported this feature.

[JF002]

I've just merged this feature in InfiniTime! It'll be available in version 1.12 ;)