Rework of Specify (was Define) phase, homepage update, installation fixes

backend

docs/INJECT_process/execute/overview.md

docs/INJECT_process/intro/overview.md

docs/INJECT_process/prepare/overview.md

docs/INJECT_process/specify/advanced_approaches.md

docs/INJECT_process/specify/exercise_specification.md

docs/INJECT_process/specify/injects.md

docs/INJECT_process/specify/learning_activities.md

docs/INJECT_process/specify/learning_objectives.md

...ECT_process/specify/learning_objectives_and_activities.md

docs/INJECT_process/specify/overview.md

docs/INJECT_process/specify/storyline.md

docs/INJECT_process/specify/tools.md

docs/INJECT_process/understand/overview.md

docs/images/00.png

docs/images/01.png

docs/images/02.png

docs/images/03.png

docs/images/04.png

docs/images/05.png