Multilingual tour for interface translation section

Follow up for #1940590: Write a multipage multilingual tour.

Problem/Motivation

Multilingual configuration is spread throughout the site. It would be useful to have a tour to help users know how to configure the site for multilingual. There should be individual tours for certain multilingual features and these can be linked together to make a multipage tour later via #1940590: Write a multipage multilingual tour.

Proposed resolution

Write individual tours for the interface translation only.

Remaining tasks

Create tour yml files for the interface translation tours:

Module page (admin/modules)
- Enable Interface Translation module (can we have a multilingual tour with interface translation module first disabled?)
Interface translation page (admin/config/regional/translate)
- Search for interface strings
- Edit interface strings
- (optional?) Import a .po file (subpage = admin/config/regional/translate/import)
- (optional?) Export a .po file (subpage = admin/config/regional/translate/export)
- Configure interface language settings (subpage = admin/config/regional/translate/settings)

User interface changes

New tours

API changes

None

Technical pointers when creating tour tips

See: https://drupal.org/node/1921152#tour-tips-tech-note for tech notes on making tour tips.