Make kdevelop-app and kdev-plugins use Qt5 resources for splash, rc, knsrc

Summary: If resources are not found in filesystem, they will be read from binary via resource path

Test Plan: Compile, remove file from 'regular' system locations, ensure related feature still functions

Reviewers: kfunk, mwolff, #kdevelop

Reviewed By: kfunk, mwolff, #kdevelop

Subscribers: kdevelop-devel

Projects: #kdevelop

Differential Revision: https://phabricator.kde.org/D529