Add support for Keyed Translation Files

[Garethp]

This adds support for Keyed Translation Files and using those Keys in C#:

• Autocomplete translation keys in "Key".Translate()"
• Navigate to that key with Ctrl+Click from C#
• Perform a Find Usages on the key from XML or C#
• Add a problem analyser to detect when an incorrect number of arguments is passed into Translate
• Add a hover over the Keys in C# to display the translation text
• If possible, show that translation text in the IDEs default language
• Add an intention in C# strings to extract a string into a translation key