Add support for adding non-String value resources

Add support for adding non-String value resources

The ResourceChooser only supported adding new Strings. This changeset
lets you add other types of value resources -- dimensions, integers,
etc. It will create a new file in res/values/ if necessary, based on
the plural form of the resource name (e.g. for "string" resources it
will create "strings.xml", etc). For existing files, it will add a new
entry to the existing file, using the same indentation as the last
top-level element in the file.

Change-Id: I09272ff52af38a8a7a059d455f398befbe0d1abc