Always show file extensions

[jeffgca]

NB: Feature requests will only be considered if they solve a pain

Summary

Most OS file explorers show file extensions. So should we.

Problem

• Files in drive don't display file extensions, but the resulting urls do.
• I can't create a .yml file in drive without having an extra fle extension added to it.
• I can't create files without file extensions.

Impact

Some confusion between drive and what users would see on disk wrt what file extensions are used.

Solution

Don't automagically add file extensions when creating files in drive itself, just let the user supply the file name including file extension.

When a user creates a new file in drive, assume it is a text file with encoding utf8 and have the user add whatever file extension they want.