Standardize on "Executable" in UI & API, do not mix with "Binary"

Summary:

• external tools might be known as binary-only, but sometimes they are inside wrapper scripts and no place really requires a compiled binary
• "executable" matches also API of Qt

Reviewers: KDevelop, apol

Reviewed By: KDevelop, apol

Subscribers: kdevelop-devel

Differential Revision: https://phabricator.kde.org/D4592