Refactor tasks

[Kraysent]

Since tasks are now used in both integration and in analysis, it makes sense to refactor some things:

• [x] Move tasks out of omtool.core.analysis and even out of omtool.core. Create omtool.tasks and move them there.
• [x] Create separate config.py for tasks and initialize them there.
• [x] Create omtool.handlers and put all the handlers for logger and visualizer there.
• [x] Move omtool.core.analysis.utils and omtool.core.analysis.visual to omtool.core.datamodel
• [x] Rename visual_task (it stopped being visual long ago)
• [x] Move AbstractTask to omtool.core.datamodel