don't allow people to send us nonsense numbers to mess up the lines of code counter

Highly unscientific proof that 1000 is a reasonable value for max lines of code:

````
mysql> select * from (select `lines` from activities order by id desc limit 1000000) as t order by `lines` desc limit 1;
+-------+
| lines |
+-------+
|   404 |
+-------+
1 row in set (0.57 sec)
````

(may need to change this in the future if we have an interface (ie js) that makes it easier to write code)
was considering that... would be a better experience (though still 'wrong') if people legitimately write 1000+ lines of code.