Move title truncation limit into a constant

app/controllers/application_controller.rb

app/views/course_editions/availability/index.html.erb

app/views/course_editions/course_participation/new.html.erb

app/views/course_editions/experiment_projects/index.html.erb

app/views/course_editions/experiment_projects/show.html.erb

app/views/course_editions/generic_projects/show.html.erb

app/views/course_editions/internships/show.html.erb

app/views/course_editions/project_preferences/index.html.erb

app/views/course_editions/projects/groups/edit.html.erb

app/views/course_editions/projects/groups/index.html.erb

app/views/course_editions/projects/groups/show.html.erb

app/views/course_editions/projects/index.html.erb

app/views/course_editions/research_groups/show.html.erb

app/views/course_editions/show.html.erb

app/views/course_editions/themes/show.html.erb

app/views/courses/show.html.erb

app/views/generic_projects/show.html.erb

app/views/internships/show.html.erb

app/views/offerers/show.html.erb