Implement tab in the descriptions of the Files app and remove dsv folder from the project

[vitormattos]

Implement in VueJS everything in the dsv folder and revmove this folder.

Suggested scenarios:

Scenario: See LibreSign in Files

• Given I'm on Files
• And I see a PDF file
• And I access the details of this file
• Then I see a LibreSign tab

Scenario: Request sign

• Given I'm on the LibreSign tab
• And I see inviting people to sign
• And I fill in with email from someone who is not on Nextcloud
• And I see the person's email
• And I click on the person's email
• And the person is added to a list
• And I can define a description of the file for this person
• And I can search for someone else to add
• And I'm looking for someone who's already on Nextcloud
• And I see the person’s name
• And I add this person
• And I define the name of the file to be signed
• And I click on request sign
• And the list is sent to the API with the file id
• Then I see "Invitation sent successfully"

Scenario: File details with pending signature

• Given I'm on the LibreSign tab
• And I’ve already asked people to sign
• And file has not yet been signed by anyone
• Then I see a list of these people and a button to remove a subscription request for someone.

Scenario: One person signed

• Given I'm on the LibreSign tab
• And someone already signed
• Then I must see in the list of who should sign that this person has already signed

Scenario: Everyone has already signed

• Given I'm on the LibreSign tab
• And everyone has already signed
• Then I should see everyone with the mark of who signed and the date they signed

Scenario: I need to subscribe

• Given I'm on the LibreSign tab
• And I have to sign
• And I see a field to enter the subscription password
• And fill in the password
• And I click subscribe
• And some password field
• And I see the status as signed
• And I see the date that the file was signed
• Then I must see: File successfully signed

Estimate: 40h

[vitormattos]

Close #159

[vitormattos]

@LibreSign/developer I added the possibility to request a subscription using nodeId, #212. Useful for requesting a file signature from the Files app.