Display current Tigris context in the shell prompt

[efirs]

Provide a command for displaying current Tigris context in the shell prompt, similar to completion:

tigris completion [bash|zsh|fish|powershell]

It can be: tigris context shell >> ~/.bashrc

and it could look like:

(tigris: my_proj1/my_branch1)$ _

also it can display an URL if it's not default:

(tigris: localhost:8081/my_proj1/my_branch1)$ _