Strip tags instead escaping on 'Commit#title' note

Further explained on https://gitlab.com/gitlab-org/gitlab-ce/issues/37616#note_40487829.

Instead escaping all chars before persisting the Commit#title on a Note this MR makes it just strip tags and avoid HTML being evaluated when showing the commit notes.

Commits list:

Captura_de_tela_2017-09-15_14.01.19

Discussion notes:

Captura_de_tela_2017-09-15_14.01.48

And for the example text on the description of this issue:

Captura_de_tela_2017-09-15_14.03.43

What are the relevant issue numbers?

Closes #37616