Enabled extra header links
Increased navibar media query max-width argument

The full-length program name in the navibar must be hidden on
slightly larger resolutions than previously, because more content
has been added to the navibar.
Corrected one localized string in navbar
Renamed models/user_course.rb as models/study_plan_course.rb
Added StudyPlan model and moved user courses and competences under it
Added index view to plans/competences

The index view allows the user to select competences to be included
in the study plan.
Changed navbar profiles link to point to competence election
Added callbacks to StudyPlanCompetence

The implementation is still buggy!
Added missing id column to study_plan_competences
Improved StudyPlan migration to make sure all users have a StudyPlan
Added StudyPlan presence validation to User model

In addition, a study plan is also automatically created when an User
is created.
Fixed User model course and competence associations
Changed studyplan/curriculum/edit view to use Bootstrap styling
Improved studyplan/curriculum/edit view redirection
Fixed StudyPlan association depedency options

This commit fixes callbacks not being properly called when
competences are destroyed.
Added postgres_ext gem as a depedency

The gem provides postgres array data type support. This shouldn't be
needed in rails >= 4.0, since rails 4.0 should have array support.
Disabled some broken links in navbar