Bump the max sizes for message limits delivered by push

[richo]

I picked totally arbitrary numbers that seemed reasonable sounding at
the time.

closes #700

in #700 (comment) @mcginty wrote:

It's just a matter of limiting auto-downloads of large files depending on the network you're on before we increase the size.

However naively, it seems that a malicious implementor of TextSecure's protocol can already bypass this limit, if the only restrictions are client side at present. Thus I propose raising the limit.

I'm totally onboard with picking other numbers, I literally just eyeballed a minute long video.

[richo]

More specifically, sending gigantor videos from Signal to TextSecure works today, so unless I'm missing something, this guard isn't protecting anything significant.

[rmueller83]

I think this is already addressed by #4019

[richo]

Oh whoops. I found my way here from #700 which doesn't mention it.