[feature] toggle broadcasting

* adds the ability to toggle broadcasting on/off 
* allows setting the specific channel name it should broadcast on.

[fix] task list last run at time format

- changes last run at timestamp format to 24 hours on task list

resolves always-open#171

[fix] use table prefix config

- update TaskRepository and Result model to use table prefix config

[fix] create task

- update create method on tasks controller to accomodate new
command list vue component

[feature] typeahead for command list

- adds typeahead component for selecting command on edit task form

[chore] update changelog

[fix] constant definition typo in service provider

The affected line was meant to fallback to the default db connection if the user does not specify one in his .env file

But instead the default connection name was being passed to define() third parameter which is meant to set whether the constant should be case sensitive or not.

PHP 7.3 added a deprecation "Declaration of case-insensitive constants is deprecated" which causes an error

resolves always-open#133

refactor : cache table prefix

- store table prefix in cache to avoid multiple and frequent database calls

fix(model) : don't concatenate table prefixes recursively

resolves always-open#122

fix(readme): fix image links