Limit express dependancy to lt version 4

express up to version 3.5.1 works perfectly, but in 4.0 beta support
for configure() was dropped. This commit fixes this dependency.
Add Procfile.

Useful for heroku deployments, or packaging with https://pkgr.io
Merge pull request #154 from Stealthii/dep-fix

Limit express dependancy to lt version 4
Merge pull request #156 from pkgr/add-procfile

Add Procfile
Ignores the enter key in the filename text field
Merge pull request #157 from swang/ignore_enter_in_filename_field

Ignores the enter key in the filename text field