Fix default banner css namespacing

[kaij]

Description

Added prefix/namespace to css class "mobile" (new: "_wb_mobile") in the default files.

Motivation and Context

As the banner CSS may get injected, this can lead to conflicts with the replayed site if a "mobile" class is used.

Types of changes

• Replay fix (fixes a replay specific issue)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added or updated tests to cover my changes.
• All new and existing tests passed.

[ikreymer]

Ah yes, this was intended for use with the framed replay, but can be an issue in frameless mode. Nice find!