Provide export of personal schedule

[odkhang]

This PR closes/references issue #162 . It does so by:

• Add 4 options in drop down for user's favorite session.

• Require user to login in order to use this feature, if User not logged in, redirect to login page.

How has this been tested?

Checklist

• I have added tests to cover my changes.

Summary by Sourcery

Add personal schedule export functionality with support for XML, XCal, JSON, and iCal formats. Require user login to access these features and filter exported events based on user favorites.

New Features:

• Introduce new export options for personal schedules, including XML, XCal, JSON, and iCal formats.
• Add a requirement for users to log in to access personal schedule export features.

Enhancements:

• Update the schedule export functionality to filter events based on user favorites.

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request introduces new data exporters for personal schedules, allowing users to export their favorite sessions. It includes changes to the export system, user login handling, and UI updates to support these new features.

File-Level Changes

Files	Changes
src/pretalx/schedule/exporters.py src/pretalx/schedule/signals.py src/pretalx/agenda/views/schedule.py	Introduced new data exporters for personal schedules and integrated them with the existing export system, including user login and favorite talks filtering.
src/pretalx/agenda/templates/agenda/header_row.html src/pretalx/static/common/scss/_pretalx.scss	Updated the export menu in the UI to include new personal schedule export options and added corresponding CSS styling.

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[sourcery-ai]

Hey @odkhang - I've reviewed your changes - here's some feedback:

Overall Comments:

• Consider refactoring the new exporters to reduce code duplication. A more generic approach that can handle both full and personalized schedules might be more maintainable.
• The XML and XCal filtering could be inefficient for large schedules. Consider filtering the data before generating the XML for better performance.
• Please add unit tests to cover the new functionality and ensure it doesn't break existing features.

Here's what I looked at during the review

• 🟡 General issues: 1 issue found
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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[sourcery-ai]

suggestion: Consider using a design pattern to reduce code duplication

The new MyFrabXmlExporter, MyFrabXCalExporter, and MyFrabJsonExporter classes all follow the same pattern of subclassing and setting favs_retrieve = True. Consider using a mixin or a factory pattern to reduce code duplication and improve maintainability.

class FavsRetrieveMixin:
    favs_retrieve = True

class MyFrabXmlExporter(FavsRetrieveMixin, FrabXmlExporter):
    identifier = "schedule-my.xml"
    verbose_name = "My XML (frab compatible)"