* Imap unread email sensor
Checks the inbox of a imap account for unread emails. Tested against
gmail.
Example config:
```
sensor:
- platform: imap
name: gmail test
user: USER
password: PASSWORD
server: imap.gmail.com
port: 993
```
* added to .coveragerc
* Code cleanup and typo fix.
* Added port range validation
* Fix lint errors
