Allow plain text expressions in where(), and() and or()

Allow plain text expressions in where(), and() and or()
This will allow custom complex plaintext sql expressions to be used, for example:
```
mytable
  .select( mytable.star() )
  .where(table.enabled.equals(1))
  .and(' DATE_ADD( mytable.lastRun, INTERVAL mytable.freq MINUTE) < NOW() ');
```