Add task navigation and loading by index

[insane-c0der]

This pull request implements the following features:

Task navigation buttons to move between tasks
Loading tasks by index
Asynchronous loading of training tasks

What?

Added "Previous Task" and "Next Task" buttons to navigate between tasks
Implemented a new input field and button to load tasks by index
Created an async function to load all training tasks on page load

Why?

These changes improve the user experience by allowing easier navigation between tasks and more flexibility in task selection. Loading all training tasks upfront enables faster switching between tasks.

How?

Modified the HTML to add new UI elements
Updated the JavaScript to implement new functions for task navigation and loading
Used jQuery's AJAX functionality for asynchronous data fetching

Testing?

Manually tested task navigation, ensuring correct cycling through tasks
Verified loading by index works as expected
Confirmed that all training tasks are loaded on page initialization

Anything Else?

This PR builds upon the existing task loading functionality and should be compatible with the current codebase. Please review the changes, particularly the new loadTask function and the modifications to the randomTask function.