Enhance string hash

This tackles both issues mentioned in #24:

1. It increases the base length from 30 to 36.
2. It uses the full sha1 hash instead of only half of it.

It avoids wasting to much characters by using base64 instead of hex encoding for the sha1 hash.
Replace constant in MonolingualTextHandler
Merge pull request #44 from wmde/stringhasher

Enhance string hash
Add TimeHandler and register it
Rewrite epoche calculation and add tests
Fix typos in field names
Updated to use DBAL
Multiple calculation errors fixed
Use before and after for calculation
There is no year 0
Update authors
Moved calculation to DataValues/Time
Merge branch 'timeHandler' of git://github.com/wmde/WikibaseQueryEngine into timeHandler

Conflicts:
	composer.json
	src/SQLStore/DVHandler/TimeHandler.php
	tests/Phpunit/SQLStore/DVHandler/TimeHandlerTest.php