Editor for surveys #78 & Display of surveys #21 - Fix for #253 #262

[DevPhilB]

Features:

• Surveys with
  • a title
  • multiple questions with small text input
  • multiple questions with large text area
  • multiple questions with single-/multiple choice(s)
  • option to customize text length (small text input) or row count (large text area)
  • optional placeholders for participants
• can be created (questions can also be deleted at any index)
• can be displayed
• can be submitted
• Validation of title, questions and choices (editor)
• Validation of missing user inputs (display)
• API for surveys (create, get=entries/results, update=submit)
• Users can now only vote for a poll or submit a survey one time

Fixes:

• Users can vote multiple times if they press F5 or reload the board (#253)
• Surveys wrong behavior on deleting fields (#262)
• Feedback from closed PR #260

To check if post & survey was created use the following SQL statement: SELECT * FROM "post" WHERE type_of_post = 'application/survey'; SELECT * FROM "survey" LIMIT 1000;

[DevPhilB]

The implementation works and looks good. The survey editor still can be scrolled to the right with a touch pad. But this is a minor problem.

The only things that aren't working are multiple choice polls. Even if the check boxes are displayed correctly, only one answer is submitted [...].

This should be fixed before the branch is merged into development.

Of course, this was fixed with 79db2fdf42b9368cb390b3c8e2b12ad9cd3888f2:

I have added also a check for duplicate answers.