Support localisation in descriptor schemas

[alansemenov]

As a user, I want to be able to localise labels and help text inside my content type so that they are displayed in correct language based on my browser locale. I also want the same localisation support in admin tool schemas so that the Launcher panel displays the admin tools in correct language.

Acceptance criteria:

• I can provide localisation key in the i18 attribute of the following fields in my content type schema: display-name (content-type), label (inputs) and help-text (inputs). For example,<display-name i18n="localisation.key">...</display-name>
• I can provide fallback value for the same fields, which will be used if localisation key (or the entire bundle) is not found. For example,<display-name i18n="localisation.key">Fallback value</display-name>
• If resource bundle for current locale doesn't exist in the application, nothing is crashes and fallback values are used
• If localisation key from the i18 attribute is not found in the resource bundle for current locale, nothing is crashes and fallback values are used
• Localisation inside admin tool schemas is following the behaviour described above and I get app names and descriptions in correct language inside the Launcher panel