Move handling of dialogs from CertificateLineEdit to SignEncryptWidget

This makes handling of multiple selected entries in the selection
dialog much easier, especially, once groups can also be selected in the
selection dialog.

GnuPG-bug-id: 5175, 5241
2 jobs for master in 12 minutes and 28 seconds (queued for 121 minutes and 14 seconds)
Status Job ID Name Coverage
  Build
failed #88384
build_clazy_clang_tidy

00:06:03

passed #88383
linux kf5-qt5 qt5.15

00:06:25

0.0%
 
Name Stage Failure
failed
build_clazy_clang_tidy Build
make[2]: *** [src/kwatchgnupg/CMakeFiles/kwatchgnupg.dir/build.make:260: bin/kwatchgnupg] Error 1
make[1]: *** [CMakeFiles/Makefile2:545: src/kwatchgnupg/CMakeFiles/kwatchgnupg.dir/all] Error 2
make: *** [Makefile:160: all] Error 2
Uploading artifacts for failed job
Uploading artifacts...
WARNING: JUnitTestResults.xml: no matching files
ERROR: No files to upload
Cleaning up file based variables
ERROR: Job failed: exit code 1