[APPS-245] Adds a Salesforce_v3 app.

This app works differently from v2 in the following ways:

1. Everything about retrieving data from Salesforce and keeping things in sync is now handled server side. Only thing the client needs to do is hit an API with a parameter to include the ticket ID
2. This app now polls every 3 seconds based on the response from the API. It also now has a lower and upper threshold limit allowing us to assure the user that something is still happening if the server side is taking longer than usual
3. We now maintain the state of the expanded result across tabs.
Re-scope variables that do not need to be global
No ifs without {}
Removed description from the translation file, as this is no longer used
Moves some display logic to CSS, rather than the template
Indentation
DRY: no need to call records.slice twice
Introduces a set up phase. Switches endpoints. Adds polling against status endpoint.
Too much marging between field labels and values
Correctly bind a timeout for `resetApp`
Removes old Salesforce app directory
Renames directory Salesforce_v3 to Salesforce
Merge pull request #1 from zendesk/v3

[APPS-245] Adds a Salesforce_v3 app.