Improve application management for file opening

[Karl-Philipp Richter]

I'd be nice to have the following possibilities when dealing the the list of applications which can open a file:

  * Remove entries for the list of applications (I know that can be done somehow by editing files in `~/.local/share/applications`)
  * Add entries with custom commands, e.g. allow opening of .jnlp files with `javaws` (this usecase is currently not covered)
  * Add a quick search text field in order to filter entries in the list of available applications in order to improve the overview

ProblemType: Bug
DistroRelease: Ubuntu 14.10
Package: nautilus 1:3.10.1-0ubuntu15
Uname: Linux 3.17.7-031707-generic x86_64
ApportVersion: 2.14.7-0ubuntu8
Architecture: amd64
CurrentDesktop: Unity
Date: Thu Jan 8 12:37:58 2015
EcryptfsInUse: Yes
GsettingsChanges: b'org.gnome.nautilus.list-view' b'default-column-order' b"['name', 'size', 'type', 'date_modified', 'date_accessed', 'owner', 'group', 'permissions', 'mime_type', 'where']"
InstallationDate: Installed on 2015-01-03 (5 days ago)
InstallationMedia: Ubuntu 14.10 "Utopic Unicorn" - Release amd64 (20141022.1)
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: nautilus
SystemImageInfo:
 current build number: 0
 device name:
 channel: daily
 last update: Unknown
UpgradeStatus: No upgrade log present (probably fresh install)

[Sebastien Bacher (seb128)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. The issue you are reporting is an upstream one and it would be nice if somebody having it could send the bug to the developers of the software by following the instructions at https://wiki.ubuntu.com/Bugs/Upstream/GNOME. If you have done so, please tell us the number of the upstream bug (or the link), so we can add a bugwatch that will inform us about its status. Thanks in advance.

[Sebastien Bacher (seb128)]

The widget comes from gtk, also it should really be reported upstream