Entirely reworked text handling pipeline

This breaks the text pipeline into the following pieces:

- input parsing (split known bracketed phoneme sections out first)

- normalization (fix spacing, numbers, abbreviations, etc.)

- phonetization (do CMUdict lookup or g2p prediction)

- sequencing (convert the symbolic representation to integer
  representation)

Each "pipeline" can have a unique combination of operations for each of
these pipeline steps.

This will grow over time.

tts/text/pipeline_components/phonetization/test_cmudict.py

@@ -0,0 +1,15 @@
+from text.pipeline_components.phonetization.cmudict import CMUDict
+from text.pipeline_components.phonetization.cmudict import DEFAULT_CMUDICT_PATH
+
+
+class TestCmuDict:
+
+    def test_lookup_success(self):
+        cmudict = CMUDict(DEFAULT_CMUDICT_PATH)
+        arpabet_sequence = cmudict.lookup('word')
+        assert arpabet_sequence == ['W ER1 D'] # TODO: Split the phonemes!
+
+    def test_lookup_failure(self):
+        cmudict = CMUDict(DEFAULT_CMUDICT_PATH)
+        arpabet_sequence = cmudict.lookup('fakeword')
+        assert arpabet_sequence == None