Applied further review comments for config folder change.
core.php: move config_inc.php include earlier in the file

This fixes a regression introduced by the new config folder commit
4b173463c2715c7dfa12dc37b6663df19930e594: global variables overriden in
config_inc.php are set to their default value in the config cache,
causing config_get_global() to return an incorrect value.

Moving the code to include the config_inc.php file back to its previous
location (immediately after config_defaults_inc.php and before
initializing the various APIs) fixes the problem.

Fixes #17263
Move env_obsolete() function to config_api.php

Makes more sense to have it here, next to sibling config_obsolete()
function, and keep obsolete.php clean with only the list of configs to
check.
Added phpdoc for env_obsolete()
Use 'info' row in env_obsolete()

To be consistent with how config_obsolete() displays the message.
Revert crypto_init() to use config_get_global()

Following fix for issue #17263, it is no longer necessary to rely on use
of global variable.
Change copyright year
Change revision number to 1.3-1

Publican 3.1.5 requires the revision number to match regex
'^([0-9.]*)-([0-9.]*)$' so with the current revnumber of 0 the build
errors.
Fix typo in Gianluca's name
Change book's author to "MantisBT Development Team"

Individual contributors will be credited in revision history.
Remove deprecated docbook tag

We don't have a publication number anyway
Add book abstract (replace default text)
Bug tracker, not Issue tracker
Add MantisBT logo

Replace the Publican default one
Updated revision history
Direct link to documentation page on mantisbt.org
Revise IRC section, add missing link to channel archives
Remove mention of contacting team for paid support
Revise version numbering convention section
Remove 'Edition'