[Request] Create go template variable for selected items in files for example

**Is your feature request related to a problem? Please describe.**
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]

Id like to perform a shell command to act on the multi-selected items in the files panel, for example batch ignore files. At the moment there's only a variable for a single file.

**Describe the solution you'd like**
A clear and concise description of what you want to happen.
Create go template variable for selected items in files for example for custom commands.

e.g.
```toil
command: 'echo {{.VisuallySelectedFiles}}'
context: 'files'
```
or something along those lines

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.
Manually ignoring single files. There's loads of other applications for providing the selected files to custom commands.