Short post content generation should be improvement

We're introduced BB-code support so just trimming the post content to 200 symbols in Post.getShortContent() is not enough.
There is a need for new algorithm to be applied not to cut BB-code apart as it may confuse user.

Consiger the following example:

... some post text [img] here comes image URL...

it may be shortened as

... some post test [im

that's certainly wrong

One more improvement should be applied:
Now the short content length is limited to 200 chars. As post content is stored with BB-codes they're included in post length calculation (although not shown as symbols). For instance, test "[b]bold text[b]" is now threated as 15-char length, but should be count as 9-char one.