Removes border from title and changes the placeholder text.

[diegoreymendez]

Description:

Removes the border from the title and changes the placeholder text to match what's described here.

Closes #372

Testing:

Test 1:

Make sure the title has no bottom border.

Test 2:

Remove the title from the demo and make sure the placeholder reads "Add a Title".

Test 3:

1. Edit the title
2. Switch to HTML and back.

Make sure the edits are properly persisted.

[iamthomasbishop]

One quick little thing I noticed when playing w/ the latest Alpha – can we set the text color of the placeholder label to $gray aka #87a6bc – same as the other placeholder text? TY in advance!

[daniloercoli]

Styling of the Title block needs to be re-worked when we migrate the Title block to use RichText.
(We can't re-use the current CSS declarations, instead we will need to move most of the declarations to props at Component level).
There is a PR open for the migration to RichText, so I guess we can migrate it, and then fix all the styling issues in another PR. #513

[diegoreymendez]

@daniloercoli - The bottom border needs to be removed anyway... so unless there's a strong reason not to merge this I'd still go ahead.

[daniloercoli]

Sorry, I meant to reply to @iamthomasbishop :)
This PR is fine to merge!

[diegoreymendez]

Thanks @daniloercoli !