XML whitespace clean up only

[jld01]

Using HTML Tidy:

tidy --input-xml yes --output-xml yes --wrap 0 --indent yes --indent-spaces 3 --indent-attributes yes --sort-attributes alpha -modify plugin.xml

Relates to #646

[Bananeweizen]

I'm not a CDT developer, but I would think twice about the sorting of attributes. At least I myself am used to finding the ID attribute as the first one, and that change would make this much harder.
Besides that, have you checked the behavior of the reformatting on multiline text string attributes? I haven't seen an example in the change, but I'm thinking of stuff like feature descriptions. As those are taken verbatim from the feature.xml, reformatting them with line wrapping or indentation always leads to end user visible changes. Similar fields might exist in plugin.xml (e.g. a perspective description).

[jld01]

Abandoning this PR in favour of one-off formatting using Eclipse IDE (#801).