Backport fixes for search external certificates

Do not prefix query with 0x and show prefix info.

This generalizes the lookupcertificatescommand again so that
it can be used with a generic query. Prefixing 0x this low was wrong
and is also not necessary at least with SKS Keyservers.

Accordingly don't show the information text about how adding
or leaving out the 0x prefix might change results. Only show
it in case a search for a keyid or fingerprint does not return
a result.

(cherry picked from commit c2a6ef0c)

Conflicts:
	kleopatra/commands/lookupcertificatescommand.cpp

Add --search command line option.

This option runs the lookupcertificatescommand with the provided
search string. This basically opens the external keysearch dialog.

The option implements the KDE 3 behavior of kleopatras
--query --external but I found it easier to understand if It is
named like the GnuPG --search option and does not mix the
"open certificate details / search on keyserver" options.

Behavior of the --query option is not documented a bit more
detailed in the help string.

CCBUG: 175980
(cherry picked from commit fcf92035)

Conflicts:
	kleopatra/kleopatra_options.h
	kleopatra/kleopatraapplication.cpp

Make "Search for External Certificates" work again

This uses the newly added search option to open kleopatra's
Keyserver search dialog instead of just opening Kleopatra.

CCBUG: 175980
(cherry picked from commit d591b2bb)

Conflicts:
	libkleo/src/ui/keyselectiondialog.cpp