#2663 - Setup - Consistently handle special characters per URL conventions

Overview
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This addresses a problem with the setup UI when installing CiviCRM with certain database credentials.
Specifically, it handles special characters more correctly.

#2663

Before
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If the database password requires any special characters (e.g. "#" or "&"), then they cannot correctly
entered.

There are two ways you might try to enter a password (e.g.  plain
`mysql://myuser:top#secret...`or URL-encoded `mysql://myuser:top%23secret...`). Neither
of these work. (The plain notation might pass the validator, but it won't be written correctly to disk.
The URL-encoded notation won't pass the validator.)

After
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You may use special characters, as long as the URL is properly encoded, e.g. `mysql://myuser:top%23secret...`