feat: update currency handling

See merge request !28

Updated the way how we handle the currency in the system. Now instead of directly getting the
user's currency or the default one, we use the getRuntimeCurrency() method. This method is likely
to return the correct currency even if the user did not set it or if there is no default currency
set in the system. This change is applied in several files including `index.php`,
`CurrencySwitch.php`, and `LangCurrencySwitch.php`. Additionally, updated `composer.json` to use
version 2.2 of `quiqqer/currency`. Removed unused code.

fix: accessibility - pagespeed insight

See merge request !26

fix: adjust paths to standard mail templates in quiqqer/core

See merge request !24

Related: #115

Related: #119

Related: coupons#17

Related: #117

This commit removes an unnecessary newline in the 'src/QUI/TemplateCologne/Utils.php' file to
maintain code cleanliness and readability. It also includes a minor change to spacing for
formatting consistency.

- Modified format for return types in declaration of functions `getAvatar`, `getConfig`, and
`getSetting` for increased readability.
- Added `ReflectionClass` usage to check for constant in `QUI\ERP\Shipping\Shipping` in
`getShippingTimeFrontendView` function, enhancing maintainability and robustness of the code.
- Adjusted the fail-safe condition inside `getShippingTimeFrontendView` to check for the existence
of the class 'Shipping' before checking for defined constant, reducing chance of errors.
- Imported `ReflectionClass` at the top of the file.

A fix has been applied in the src/QUI/TemplateCologne/Utils.php file. A condition has been added to
check whether the PRODUCT_FIELD_SHIPPING_TIME constant is defined. If not, the function will return
false to prevent any potential errors.

Several changes have been made, primarily around checking the existence of methods and classes and
removing unnecessary comments.

- Method checks have been introduced to ensure the `getCachePath()` method exists before calling it.
- Removed invalid phpDocs, e.g., @var $Site Site and @var $Project Project
- Fixed typing to align return types and updated a factory method to check class existence.
- Added variable definition comments in the settings.css.php file for clarity.

Related: #114

Related: #116

feat: show product images in basket setting

See merge request !23

Related: #111

Add QUIQQER Tooling

See merge request !15