Fix LANG-948

Hi all!
This is fix for bug LANG-948.

Changes with explanations:
1) Method ```ExtendedMessageFormat.appendQuotedString()``` returned when finds first quote character. This is obviously wrong because quoted string start with quote character and method must consume whole quoted string. I added handling of first quote character at the beginning of method. Also, it doesn't make sense to handle escaped quotes because ```super.applyPattern(stripCustom.toString())``` will called below in ```applyPattern()```. Thus, last argument should be ```false``` when calling ```appendQuotedString()```.

2) Quoted string must start with quote character in ```appendQuotedString()```. And at this moment method is used this way. I added assertion to check and document this.

3) Thus, method ```appendQuotedString()``` is called with last argument always ```false```. It doesn't make sense to handle escaped quotes in ```appendQuotedString()``` because they will be handled in ```super.applyPattern()```. Thus, I deleted this parameter and code for handling escaped quotes.