This commit refactors several things in "runtime/permissions" module:
- splits it into "mod.rs" and "prompter.rs"
- adds "PermissionPrompter" trait with two implementations:
* "TtyPrompter"
* "TestPrompter"
- adds "before" and "after" prompt callback which can be used to hide
progress bar in the CLI (to be done in a follow up)
- "permissions_prompt" API returns "PromptResponse" enum, instead
of a boolean; this allows to add "allow all"/"deny all" functionality
for the prompt
