Remember public link password on page refresh (alternative)

[PVince81]

Simpler alternative to #4083

Description

When refreshing the page in the file list of a public link share,
the user doesn't need to enter the password again. This only applies for the current page
and the password is forgotten by the browser again upon closing or switching to another site.

Related Issue

Part 8b of owncloud/product#231

Motivation and Context

How Has This Been Tested?

After entering password on public link page:

• TEST: refresh the page doesn't ask for password again
• TEST: closing page and opening the URL again asks for the URL again (so password is forgotten correctly)
• TEST: change public link password to create a discrepancy with saved one: password is asked again

Screenshots (if appropriate):

Types of changes

• 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)
• Technical debt
• Tests

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation ticket raised:

Open tasks:

• ...

[LukasHirt]

LGTM 🚀