Maximum attachment size support - for one and all files

[KamilaHasanbega]

The attached file(s) max size limit needs to be set at 25Mb (right now there is no size limit).

[KamilaHasanbega]

I made this work by stopping the attachments from being added, if filezise + array size of pervious attachments exceeds 25Mb, but now I have a few issues UI related:

• I show the warning that the file(s) cannot be added once they exceed 25MB when the user tries to upload it/them below the attachment-send-cancel bar. (Is that the right behavior?)
• As for now, I only disable the button once the previous files added, add up to 25MB, but that needs the file to be exactly 25 Mb otherwise it doesn't happen (as if < there is still space in the array) - Is that the right behavior regarding UI or should I set a range, say 24.5-25 mb -> attach button disabled? @koto @aesdeluca

[KamilaHasanbega]

Fixed at #33