Rename deviceinfo_date to deviceinfo_year

The deviceinfo_date property is supposed to contain the release date of the device. But we don't use that property in a consistent way:

• Of the 175 devices in pmaports, only 16 devices (~9%) set deviceinfo_date.
• Only 3 of the 16 devices set a standard date format like 2012-12-06.
• Others just set the year (e.g. 2010), or July 1, 2014, or 20140501 or even 04/29/2017 (Malaysia)

I think the two main reasons for this are:

• The format of the property is not properly documented.
• It is usually quite hard to figure out the exact release date of a device. The year is usually easy, sometimes you can figure out the month - but the date is often hard to find.

In my opinion we should:

• Rename deviceinfo_date to deviceinfo_year for all existing devices in pmaports.
• Mark deviceinfo_date as deprecated in pmbootstrap.
• Go through the wiki pages of all existing devices and fill deviceinfo_year with the release year.