Add i18n support to the unity-scope-tourism-shanghai-* scopes

[David Planella]

The unity-scope-tourism-shanghai-* scopes need to be internationalized for translations to be displayed. In a nutshell, that means:

1. Marking strings as translatable in the code and adding the necessary gettext headers
2. Adding CMake rules to a) extract translatable strings from the code and put them into a .pot file and b) build the binary translation files (.mo) from the textual translation sources (.po) provided by translators
3. Set up translations in Launchpad so that translators can do their work and that translations are automatically committed to the code.

I can take care of 3. once the first two points have been addressed. For guidance on 1. and 2., these branches can be used for the implementation:

https://code.launchpad.net/~mhr3/unity-scope-mediascanner/i18n-enablement/+merge/217389
https://code.launchpad.net/~dobey/unity-scope-click/translated/+merge/214182
https://code.launchpad.net/~dobey/unity-scope-click/no-auto-pot/+merge/217672