Make keywords and some constants lowercase

According to the PSR-2 standard the PHP constants
- NULL
- FALSE
- TRUE

should be lowercase.
Add a blank line before return statements

Though this is not a part of PSR-2, it is a part of the Symfony
conding standards and it is a very popular convention.
Remove space between opening parenthesis and "!"
Put a space between function keyword and opening parenthesis
Remove spaces between opening parenthesis and type hints and &
Put class bracket on the next line
Remove extra blank lines before class closing brace
Put every argument of a multi-line call on a new line
Shorten long lines
Declare visibility on all methods
Fix function braces
Reduce multiple blank lines