Features/default EmailTemplate for HalfYearProcess and HalfYearProcessOverdue

See merge request !826

Added waive to volunteer xlsx

See merge request !825

feat(semester-process-volunteer): add nested attribute form table to select volunteers for semester-process

- in order to have elegible volunteers to be rebuilt for the changed semester daterange

feat(semester-process-volunteer): add controller, routes, policies and basic scaffold for views to the model

Feat/semester process volunteers initial builders before creation

Closes #459

See merge request !823

- takes query of elegible volunteers and then builds SemesterProcessVolunteer for each
- if array of volunteer ids is passed, it will only build SemesterProcessVolunteer for these

- if passed from form input, it can build the correct semester that was passed from form input

- so that it can be treated as a child of this in forms
-

- relations to all hours with meeting date within the semester
- scaffold empty semesterFeedback record for each mission related
- build the SemesterProcessMail.kind == :mail for the initial mail

feat(semester-process-volunteer): builder that assigns the elegible missions from the volunteer to the SemesterProcessVolunteerMission join table relation

add attr-acessor for selected, in order to be able to filter form selected volunteers on select in form

Chores/create specs for semester process elegibility scopes

Closes #459

See merge request !824

feat(semester-service): add service that delivers semester date ranges and lists for forms

See merge request !822

fix(volunteer-semester-process-elegible): fix have_semester_process with doing subselect, because it didnt work otherwise

feat(semester-process-elegible-volunteer): add method semester_process_eligible that joins and groups the relevant scopes for semester process volunteers

feat(semester-process-elegible-volunteer): add scope that selects volunteers that where with active assignments or group assignments within the given semester

feat(semester-process-elegible-volunteer): add scope that gets volunteers wit a assignment or group assignment that has started, ever

feat(semester-process-elegible-volunteer): add scope that returns volunteers that dont have a semester process for given semester