Cleanup xml

[nielsbasjes]

This touches only the XML form of the specification and is intended to resolve unclear parts and fix bad xml:

• All points have an explicit len indicating how many modbus registers must be read.
• Trivial attributes values that are the same as the default specified in the schema have been removed (like access="r" and mandatory="false")
• The attribute units="" is meaningless and removed
• All blocks have an explict type (fixed/repeating)
• Because I used custom software to do this cleanup all attributes are in the same order everywhere. In fact: I parsed the json and generated the xml from that and then manually cherry picked and verified the changes I'm proposing here.

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