Add multiple account support

[gurland]

Implement ability to work with multiple accounts.

For CLI interactive mode we have to:

• Remember last successful login and display that session as default
• Display list of all available sessions
• Let the user to add/remove sessions

For default argument based CLI (should be implemented in #11) simply add argument with name/path to client session file.

Sessions in pyrogram are stored in .session files which are simply SQlite database files. https://docs.pyrogram.org/topics/storage-engines.

[xanoni]

As a workaround, I just have a bash script swap out the Config.session file before I invoke the program.