Checkstyle config to check tabs in java source files only
PrefixType refactor to hide RegExp.

It now expose a method to check if a prefix is found in a given string,
hiding the implementation details.
Added enum to list the supported prefixes.

This can be useful for client applications needing to show to the users
what are the available prefixes.
Simple style adjustments.

Removed few unused imports, removed a sysout, reformatted some class.
Replaced StringBuffer with StringBuilder
Added smoketest for ExtractTextByPages.