split CFFCharset to two classes

[valerybokov]

Hi! I found TODO in CFFCharsetCID class and decided to implement it. Hope you find this helpful.
Several notes:

• I created CFFCharsetCID and CFFCharsetType1 (new classes) as package private because CFFCharset is abstract.
  Also, I set them as non-abstract because Format0Charset is not abstract. But if you think they should be abstract, I will think about how to change it.
• I extracted the EmbeddedCharset from CFFParser because it is big class. I don't like to use big inner classes and CFFParser has too many inner classes. But if you want you able to move it (make as inner).

[THausherr]

Andreas is currently busy with refactoring CFF, so it's better to comment there, so that you don't interfere with each other (this applies also to your recent comment in #107)
https://issues.apache.org/jira/browse/PDFBOX-5143

[lehmi]

I'm going to look into this as well as the others proposed changes in the CFFParser area