fix: prevent to initialize Triggers twice before window is loaded

[ncoden]

Description

Check if Triggers is already initialized just before it should be initialized, once the window is loaded.

Motivation and Context

For the following code:

...
Triggers.init($, Foundation);
Triggers.init($, Foundation);

Triggers will be initialized twice when the window will load.

Types of changes

• Documentation
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing
  functionality to change)

Checklist (all required):

• I have read and follow the CONTRIBUTING document.
• There are no other pull request similar to this one.
• The pull request title is descriptive.
• The template is fully and correctly filled.
• The pull request targets the right branch (develop or support/*).
• My commits are correctly titled and contain all relevant information.
• My code follows the code style of this project.
• I have updated the documentation accordingly to my changes (if relevant).
• I have added tests to cover my changes (if relevant).
• All new and existing tests passed.