[Input] Selectors must allow multiple inputs

[zeh]

Selector inputs can be passed as part of a command, but they're separated when submitted (equivalent to a space before and after). Instead, the commands need to be smarter and only add a space if one is really desired.

This will allow us to have selectors that are only part of a parameter. For example, when resizing an image, we need to pass something like w:h, where w and h should be different inputs, with no space between them.

Requirements

• Command input conversion must follow the convention as written in the command definition (only separate where spaces are used)
• Add commands or adapt using commands as needed (e.g. resizing)