[ENH] Improve toggle button styling and functionality in tiki collapse module

This merge request improves the toggle button in the collapse module template by enhancing its styling and functionality. Key updates include:

• Adding styles to toggle "Show" and "Hide" text based on the button's collapsed state.
• Fixing the issue where the button appeared as a black dash without text.

Example used:

{MODULE(module=collapse,target="#hello") /} {DIV(id="hello")} Bonjour {DIV}

Before:

After these changes:

Collapse feature-After.mp4