Settings: Add a search field for shell commands

[Taitava]

Depending on usage, some vaults may contain tens of different shell commands. Finding a specific shell command in the settings can currently be quite hard at times.

A quick mockup of how a shell command search field could look like:

(The search is not really working here, it's just to demonstrate how the field could be placed in the UI.)

When typing text, the visible shell commands would be limited to the ones matching the search term. Properties where the search would look for:

• The actual shell command.
• Alias