add functions:
1. select new drug when create new fixedrecipe
   can only add the drugs from the last shown page
2. can delete the existed drug in fixedrecipe
It can patch!
I don't know why I can't add drug when I create a new fixedrecipe and did no edit.
And if a add any field in fixedrecipe I can add new drugs.

I have been in a wrong way for a long time.
In fact although you use the same drugid samd frepid, if give the item a new id, the old one will be deleted.
that's really easy if you get into the right wary at first.
now I fix that problem: can't add drugs if you haven't edit any field when you create a new fixedrecipe.
Merge branch 'manyToMany' into develop
keep the checked checkbox checked after turn to other pages.
Merge branch 'manyToMany' into develop
give drug_name when edit a fixedrecipe
Merge branch 'manyToMany' into develop
many to many is approximately finished.
some bug and risk is recorded on redmine.