add field parent_id in tasks

for sub-task feature
sub-task feature

updated current working version
this is all so far, but more to come
add field sibling_order in tasks

for later use
preset columns/fields for tasklist

include parent
made some small fixes around missing logo and version will be 1.0 instead of 1.0.0
Sub-Task / Super-Task

renamed for clarification and distinction:
- "parent" to "super"
- "child" to "sub"
added theme "CleanFS_wSubTs", restored theme "CleanFS" to default
rename "parent_task" to "supertask"
cleanup & fix

rename "parent" to "supertask"
rename "child" to subtask"
delete *.bak files
merged in Oliver's subtasks code