Do not report notices to error log

Hi!
I'm using the latest Piwik 2.5.0 and I'm seeing lots of *notices* in my php error log (they are generated by plugins).
I guess intended behavior was to ignore notices, but there are `E_ALL | E_NOTICE` everywhere.
```php
var_dump([E_ALL, E_NOTICE, E_ALL | E_NOTICE, E_ALL & ~E_NOTICE]);
/*
array(4) {
  [0] =>
  int(32767)
  [1] =>
  int(8)
  [2] =>
  int(32767)
  [3] =>
  int(32759)
}
*/
```
:wink: