Remove newlines from XML responses
Remove newlines from XML responses

This is a second attempt at resolving the issues with producing an XML consistent with what is produced from AWS (i.e., no spaces/new lines between tags). Another attempt (https://github.com/spulec/moto/pull/2205) is currently failing in tests.

This attempt uses precompiled regex patterns as class attributes of the `_TemplateEnvironmentMixin` to remove trailing spaces and newlines after a `">"`, and preceding newlines/spaces before a `"<"`. This *explicitly* wasn't done with a single regex to ensure that even things like `"...<ID>\n      12345\n    </ID>"` are properly collapsed.
spulec/moto,spulec/moto,spulec/moto,william-richard/moto,spulec/moto,william-richard/moto,spulec/moto,william-richard/moto,william-richard/moto,william-richard/moto,william-richard/moto,spulec/moto