fix: do not decode encoded URLs

[pdecat]

This PR avoids breaking URLs where some query string parameters are URL encoded.

Without this change, such URLs are altered, e.g.:

• http://example.com/query?q=random%20word

is passed to the browser as:

• https://example.com/query?q=random/word

This alteration breaks some links such Amazon package tracking links received by email.

To fix this, this PR makes use of the [G_URI_FLAGS_ENCODED](https://docs.gtk.org/glib/flags.UriFlags.html#encoded) flag.

[sonnyp]

Feel free to add yourself to contributors in about.js too

[pdecat]

Done, thanks @sonnyp! :rocket: