Fix notice when empty section title in task

Problem with this patch: there are 3 sections available but you are not required to use them all. However, with this patch you would always need to add three sections with a title.

Changed title, fix would be to prevent the notice in the first place.

Patch attached.

I fought that a required FC-item field can be required if the FC-field itself isn't required.

The problem is, that there are always 3 items printed, instead of 1 or something equal to the used items, with a maximum of 3.

Also with the patch #5, a list item won't be printed and this could be a usability/accessibility issue.

A validation on title is in my opinion the way to go, when the body of the FC-item isn't empty, the title is required.

Or.. there is only one FC-item with an 'Add more' button with a max of 3 and FC-item-title-field is required.

@Tessa: the add more functionality with a max of 3 would be best, in that case the title could be required.
There is a RTBC patch for field_collections to allow for an add more button:
https://www.drupal.org/node/1788222

However, I'm not sure if this patch takes into account a maximum number of items set. Worth testing though!

If the customer want to create a very short task, don't use a section.

A section is only needed for complex tasks where headings are needed.

Why titles need to be required is because if you have 2 or more sections, you can skip to section 2 or 3 with the small in-page menu very helpful on small screens like phones). Also this menu can be use to style the sections as tabs on wider screens.

I've created a follow-up for these improvements: #2757727: Improve sections UX so the patch in #5 can be committed.