feat: Enhance task management with start and end time handling

- Added functionality to calculate task duration based on provided start and end times.
- Implemented logic to derive end time from start time and duration if only start time is provided.
- Updated task creation and update APIs to handle new time fields.
- Introduced a modal for editing tasks with flexible time and duration inputs.
- Improved UI for task creation and editing, including better handling of time inputs and duration selection.
- Added two-way synchronization with Outlook for task updates.

admin.php

@@ -542,7 +542,9 @@ require_once __DIR__ . '/includes/header.php';
                             <div>
                                 <label class="block text-[11px] font-medium text-slate-600 dark:text-slate-400 mb-1">Standaard tijdslot</label>
                                 <select name="default_task_duration" class="w-full bg-white dark:bg-[#111622] border border-slate-300 dark:border-slate-700 rounded-xl px-3 py-1.5 text-xs text-slate-900 dark:text-white focus:outline-none focus:ring-1 focus:ring-indigo-500">
+                                    <option value="10" <?= $workdaySettings['default_task_duration'] == 10 ? 'selected' : '' ?>>10 minuten</option>
                                     <option value="15" <?= $workdaySettings['default_task_duration'] == 15 ? 'selected' : '' ?>>15 minuten</option>
+                                    <option value="20" <?= $workdaySettings['default_task_duration'] == 20 ? 'selected' : '' ?>>20 minuten</option>
                                     <option value="30" <?= $workdaySettings['default_task_duration'] == 30 ? 'selected' : '' ?>>30 minuten (Standaard)</option>
                                     <option value="45" <?= $workdaySettings['default_task_duration'] == 45 ? 'selected' : '' ?>>45 minuten</option>
                                     <option value="60" <?= $workdaySettings['default_task_duration'] == 60 ? 'selected' : '' ?>>60 minuten (1 uur)</option>