Lazy serve: Fix improper handling of incomplete active urls

[ryoarmanda]

What is the purpose of this pull request?

• Documentation update
• Bug fix
• Feature addition or enhancement
• Code maintenance
• Others, please explain:

Bug reported and acknowledged in #1522 (comment).

Incomplete urls are defaulted to index.md in the path specified, e.g. hostName/userGuide serves hostName/userGuide/index, though the request URL is still referring to hostName/userGuide. This results in getActiveUrls returning just /userGuide, which will be stored as userGuide to the current opened pages list, and thus any file change to the actual file userGuide/index can not be detected and rebuilt accordingly.

Overview of changes:

• Adds a processing step of active urls retrieved from live-server before passing it to MarkBind's opened pages list, to append index on every incomplete urls.

Anything you'd like to highlight / discuss:

Testing instructions:

• Try opening 127.0.0.1:8080 (without /index)
• Edit root's index.md
• Verify that MarkBind correctly logs that the current opened pages list is index.

Proposed commit message: (wrap lines at 72 characters)
Lazy serve: Fix improper handling of incomplete active urls

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Checklist: ☑️

• Updated the documentation for feature additions and enhancements
• Added tests for bug fixes or features
• Linked all related issues
• No blatantly unrelated changes
• Pinged someone for a review!

[wxwxwxwx9]

LGTM 👍