Simplify the pipeline in sys_initloadpreferences() so that we read the preferences directly using plutil now.

This is done by importing the config data using 'defaults import' in
one go, which is *much* faster than the previous implementation which
invoked the shell to run 'defaults write' for each individual key.

We use 'defaults export' rather than 'defaults read' to grab the prefs data on OSX now, which loads the prefs much faster and also properly deals with filenames containing UTF-8 characters.

Otherwise search paths from old program versions installed in different places may keep piling up, eventually causing issues when submitting prefs data because of buffer limits.

Turn the user config dir (~/.pd-l2ork on Linux) into a #define so that it's easier to patch it up when needed.

Add support for loading and storing the MIDI API preference (commit 516eba76 from vanilla by aib <aibok42@gmail.com>, slightly edited.

Keep track of the number of audio and MIDI device entries in the preferences, to avoid zombie entries on Mac and Windows. Proposed fix for #213, needs testing on Mac and Windows.

for reading preferences on Windows, try HKCU first, then fall back to HKLM. For writing, only write to HKCU

first draft of saving the preferences, including the gui preset (still won't write to file for some reason)

*further improved naming convention for settings files (default.settings and user.settings), cosmetic improvements to the indexing prompt of the help browser dialog.

*updated file locations and made names more consistent across all folders (everything now uses pd-l2ok instead of pdl2ork). Placed user settings into ~/.pd-l2ork/ folder and renamed to simply settings, placed xapian search database for the browser inside the ~/.pd-l2ork folder.

*updated most of the audio API to the latest version (with the exception of ALSA and JACK which are partial until our improvements can be merged and/or new implementation of JACK thoroughly tested to ensure we like its default behavior)

forgot to add another change to make it in sync with 0.43+ branch where real-time is default behavior.

reverted 0.43 backport as its implementation seems unstable when trying to (re)connect to jack via audio properties. Fixed a bug where closing jack while having DAC on would hang pd.

backported audio driver support from 0.43 and the pd/extra folder with supporting fixes/merges where needed. Removed outdated expr-help file in favor of new documentation.