Add support for detecting Contour terminal in title() function

[christianparpart]

Standards checklist:

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• I have read the contribution guide and followed all the instructions.
• The code follows the code style guide detailed in the wiki.
• The code is mine or it's from somewhere with an MIT-compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable and I have tested it myself, to the best of my abilities.
• If the code introduces new aliases, I provide a valid use case for all plugin users down below.

Changes:

Contour Terminal is is supporting OSC 1 and OSC 2 as well as host programmable statusline, which can be controlled via terminfo entries tsl / fsl / dsl. OMZ seems to use tsl/fsl to fallback-set the window title, and that is heavily confusing. So this change ensures OSC 1 + OSC 2 logic is used, to streamline this change with most TEs.

Other comments:

I personally think that the host programmable statusline is a bad start to simply show that string is probably not the best choice to begin with. Despired having rare support for it. :)

[carlosala]

Thanks!