Merge config files (#1487311).
Now we have defaults.inc.php and config.inc.php.
Renamed $rcmail_config to $config. Old naming and old files are supported
for backward compatibility.
Add defaults.inc.php file (missed in last commmit because of .gitignore)
Flag config as 'legacy'; remove config file switch
Enable legacy mode: allow running with old config files and log warnings every no and then
Prepare config migration:
- Show warning in installer and hints how to migrate
- Let update.sh create the new config file if legacy config is detected
- Provide a sample config file for manual configuration
- Define a list of options which always should be written to local config
Preserve comments and order from existing or default config files
Improve update.sh script; fix bad wording
Avoid fatal errors if session support is missing; This shall be displayed in the first step
Fix parse error from last commit
Set z-index for messagelist and fixed header copy; fix overflow settings; removed unused definitions
Enable fixed message list header in classic skin
Right-align size column header
Simplified logic of finding non-existent but subscribed folders. Should be more reliable and (might be) faster now.
Merged configuration refactoring from 'dev_config' branch back into master (#1487311)