Add <phrase role="style:..."> support

[tomschr]

Supports the following styles:

• "uppercase" (only text, no child elements)
• "lowercase" (only text, no child elements)
• "sentencecase" (first character is capitalized, rest is unchanged) Supports also nested child elements to some degree

This can be used for entities which first character is lower case, but the entity is used at the beginning of a sentence.