Add OnPropertyValueCondition annotation

This commit adds a new conditional annotation that checks if a
property has a given value. This allows to replace constructs
such as

@ConditionalOnExpression("'${app.myProperty:foo}' == 'foo'")

to

@ConditionalOnPropertyValue(property="app.myProperty",
        value="foo", defaultMatch=true)

Which is definitely more verbose but has the following advantages:

1. Works by default if the actual property in the environment is
   a bit different (i.e. my-property)
2. Works if the value of the property has a diferent case (FoO or
   FOO would match)
3. Gives a precise reporting in the auto configuration report

The defaultMatch flag is meant to mention that the condition should
also match if the value is not set; the auto-config report would
also have an explicit report about it.

Fixes gh-1000