New core::config('general.disallowbots') to block bots & crawlers

+ to add in DB upon upgrade?

```sql
INSERT INTO `oe_config` VALUES (
`group_name` = 'general',
`config_key` = 'disallowbots',
`config_value` = '1') ;
```
Merge pull request #279 from RedActin/metas_norobots

New core::config('general.disallowbots') to block bots & crawlers