APPS-1779 Simple time submission

:koala:

This PR intends to add simple time submission functionality, so the agents can submit time log as a single number which represents how many minutes they spent on the ticket.

Translations are in https://github.com/zendesk/timetracking_app/pull/39

/cc @zendesk/quokka 

### REFERENCE
- [JIRA APPS-1779](https://zendesk.atlassian.net/browse/APPS-1779)

### RISKS
- N/A
As in the function isn't that safe. parsing a non number will give zero but so will entering 0 which is a valid number. Maybe it makes sense in this case, but it's odd because we're not using the default at all.