[add] epx 'call' js/php functions for non-api calls

-fascilitates direct db calls
-amend php POST handler, limit function calls to known set
-added 'settings path' input
-add overflow scroll to settings section
[add] database layer and test call

-support for postgre databases only
[add] epx 'getGroupsMappers' function to display mappings
[imp] ep/epx 'call' wrapper status output control

-push 'verbose' parameter back
-add 'append' parameter
[fix] group addition/deletion select control sync
[sup] refactor 'ep_padsType' -> 'ep_padsShow'
[imp] make pad type display clearer

-display 'group (public)' pad type by default
-remove 'All' entry from empty select control
[imp] break controls buttons into sections

-tighten button spacing
[imp] dynamic height for vertical sections

-use 40%-60% proportions for the two distinct vertical sections
[sup] update README.md
[fix] groupID gid inconsistency

-replace all with generic 'id' variable as it's better boiler plate
[fix] control bar overlay and overflow
[add] select pads per group
[fix] data code and message for empty database result set

-set 'success' values, e.g. code: 0, message: 'ok', for database
queries returning no records, e.g. delete queries
[add] add/remove authors, and list authors of a group's pads
[add] global author list

-refactor 'epc_authors' -> 'epc_authorsOfPads'
-add new epx 'listAllAuthors' and 'getAuthorMappers' calls
[imp] error handling for ajax calls

-standardise ajax wrapper usage to expect js 'undefined' for failure
-cope with ajax call to unsupported methods
[imp] remove superfluous form element wrapper
[imp] remove fixed settings / info width restraint

-remove status container's 100% width + fixed margins setup and
rely on div's 'display: block' default 100% expansion in natural
rendering flow
-adding padding to adjacent containers to cover the bleeding
from 'status' caused by the necessity to specify '100%' height to
enable vertical overflow
-wrap lower 'select' containers in an absolutely positioned div to
account for the above padding hack
[fix] footer background image for opera browser