Enforce consistent usage of quotes

[erikbosch]

We have a recommendation that single quotes shall be used for string literals. But it is not consistently used. In most cases it has no practical consequence - the *.vspec files are based on Yaml and there can be a slight difference in meaning between single and double quotes, but should for most of our usage not matter.

Idea:

• Change syntax/rules so that single quotes are needed
• Add a feature in vss-tools so that an error (or warning) is given if quotes are not used as expected. Like checking all string literals.

But the philosophical question here is:

• Do we want Yaml to be "part" of VSS *.vspec syntax, i.e. that all Yaml-constructs for quoting/escaping are valid in VSS as well. The advantage with this approach is that we do not even need to care as long as we start with using a Yaml parser and only sees the result after parsing
• Or do we want VSS to have it's own syntax, which just "by coincidence" happen to be an "extended subset" of Yaml.?