Add "Add/Improve GUI Translation" in the main Help menu

[slodki]

A simple link to Crowdin (or README/wiki with detailed instructions - #1345) should be enough.
Just below existing Report a Bug.

[slodki]

1. Help → Improve translation

   • should open simple pop-up with instructions like this:

     You can easily improve translation strings in MMEX GUI using only web browser devoting a few minutes to translate. All translation tasks in the project are managed on the Crowdin platform.

     1. Open Crowdin page in your browser
     2. Create account / log in
     3. Select target language and mmex.po file to translate GUI strings
     4. Type untranslated or mistranslated string in the search field on the left, select one of displayed items below
     5. Add or fix translation in the center window
     6. Click the Save button
     7. When the translation or fixes are verified, they will be added to the application.

     [ CLOSE ] [ OPEN IN WEB BROWSER ]

   • ❓ linked to the current GUI language file https://crowdin.com/translate/moneymanagerex/470/en-language or to general tab for language https://crowdin.com/translate/moneymanagerex/language

   • ❓ how to do reverse-mapping from MMEX locale to Crowdin language id

2. Add Add missing... option as the first item under View → Switch Application Language with similar pop-up but

   • inform there can translation on-going at Crowdin platform already
   • describe the quality criteria to be met by translation to be added to the application package
   • steps how to start translation for a new language

[vomikan]

https://user-images.githubusercontent.com/6836805/53188845-3dc55100-3617-11e9-865d-1081955dc101.png