Add option to list locks

To list locks:
/timereport lock list

Also support for specify year:
/timereport lock list 2019

Add helpful message for lock action

When user forgets to provide an argument

Add more help messages

Show specific help for all actions

1.13.3: Upgrade python #129 (#157)

Use python 3.7 in Travis and in pipfile

1.13.2: Refactor creating block messages for list action (#155)

Add Slack class methods for creating block messages in a generic way to make it easier to build slack block messages.
Remove the old create_block_message function.

Implement edit action

Merge pull request #146 from codelabsab/#12-implement-edit

Refactor _valid_number_of_args

Improve edit action

Improve _edit_action (#142)

* Improve edit action

* Use parse_date function
* Send feedback if wrong date format
* Send feeback if date range (not supported for edit)
* Check if month is locked
* Remove unnecessary test

#12

Implement checking lock for add action

Check locks for add action (#140)

Add action will now check if one or more months are locked in the given date range before adding

#100

Implement lock for delete action

1.11.0

Implement lock check for delete action (#139)

Refactor factory

Fixes #137 refactor factory (#138)

* Renamed json_factory -> factory
* Remove old factory
* Add format_str as configurable item
* Move date_range into helpers.py
* Add new function validate_date
* Refactor submit_message_menu

#137