Improve the tagging preset schema

[gaben]

I plan to add a new description to the XSD fields, as well as some extra validation, if possible (e.g. object types [node, way, relation]). While the schema is designed to be flexible, it is also error-prone. For almost 15 years, the fact that it contains unused parameters went unnoticed. Examples:

• delete_if_empty was removed in 2012 (r5155): ​https://github.com/JOSM/josm/blob/bdc651ba9185db66d751a9f81922a2a89ac486dc/resources/data/defaultpresets.xml#L3006-L3038
• values_i18n="false" never did anything? ​https://github.com/JOSM/josm/blob/bdc651ba9185db66d751a9f81922a2a89ac486dc/resources/data/defaultpresets.xml#L295
• and more

More stringent validation enabled me to fix r19563, which had also gone unnoticed for some time.

The patch will follow soon, hopefully.

[stoecker]

Problem is the I18n tags which prevent the checks for unused values.