ctf: Put Antlr-specific exceptions in a separate class

ctf: Put Antlr-specific exceptions in a separate class

Since CTFReaderException is in the public API, any external
plugin using it would have had to import the antlr-runtime
packages.

By isolating the Antlr-specific stuff in a separate, non-API
class, external plugins can happily continue to use
CTFReaderException without fear of leaking dependencies.

Change-Id: I27cccd60dd0ad1ca51a91c10b067a19b07c24f2e
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/12224
Tested-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
IP-Clean: Matthew Khouzam <matthew.khouzam@ericsson.com>