#2040 Update database schema for certificates:
- Add active flag to quickly identify the current active certificate (highest version number)
- Add created_at timestamp
Merge branch 'dev' of https://github.com/studer-raimann/Certificate into dev

Conflicts:
	plugin.php
#2026 Added searching for certificates, need to check how permissions are handled. The table should use external sorting and segmentation
Update srCertificate::getCertificateData method
Make srCertificateTableGUI more generic so that this table can also be used to display certificates on per definition (inside a course). Use external segmentation and sorting
Use srCertificateTableGUI also for displaying certificates in courses
Just a small PHP Docblock addition
Update README.md
- Refactoring of certificates table, add possibility to display certificates from a given user
Factor out some logic from form GUI classes to the settings models (still it would be better to factor out each setting into its own class)
Refactor Settings in order to introduce custom settings objects
- Type Settings and Definition Settings have an abstract superclass
- Changed property 'default_value' to 'value' for type settings, for consistency
- Updated the above change in database with new update step

Still the settings need to be refactored regarding how the forms are built at some time
Update references to renamed methods "getDefaultValue()" and "setDefaultValue()" removed with last commit
Implement Custom Settings for types and definitions
- Pass custom settings to PDF renderer, e.g. Jasper
- Add GUI for user to list all certificates
- Add GUI for administrators showing certificates of all users ( TODO Permission check based on plugin configuration)
- Refactor Standard Placeholders
Merge branch 'dev' of https://github.com/studer-raimann/Certificate into dev
Refactoring: Config object uses ActiveRecord, Certificate plugin only accessed as singleton
- Add new config options: Selecting roles allowed to administrate Certificates and Certificate types
- Do permission checks according to the new config options
- Remove some unused/old files
Remove commented code
Bugfix, reference new config object
Bugfix from previous bugfix ;)
add some requires as they were missing on my installation.