Fix handling of multi-line string literals

Multiple issues:

- CeylonExpressionTransformer didn’t re-align the string, so it would
  produce something like

    anonymousAnnotation = StringLiteral("""The run function.

    Prints “Hello, World”.""");

- RedHatTransformer didn’t generate additional indentation to align the
  lines
- stringLiteralToCeylon didn’t strip the additional indentation away to
  re-align the lines

Also fixes the recognition of prefixed identifiers.
Remove SimpleTokenFactory

It generated wrong lengths.
Test identifier prefixes in assertEquals

Identifier.equals ignores usePrefix, so we test it ourselves here. (This
is the reason for the SimpleTokenFactory removal in the previous commit;
now we can FINALLY be sure that this actually works.)