Disable on large file

An attempt to resolve #1238. I did it on the client side because did't seem right to send a large file from the client to the server just to be discarded.

I signed the CLA
That low? I mean, larger file size means that probably there is more code than is needed for a single translation unit, but 100kb seems a little low. Why not match the size of the max request, which from [ycmd/handlers.py#L48](https://github.com/Valloric/ycmd/blob/master/ycmd/handlers.py#L48) would be 1000Kb, for a default?