Editing user prefs when no project exists triggers error

It was not possible to update a user's preferences when no projects
exists (e.g. right after installation), Mantis triggered application
error 20.

We now omit 'All projects' from the default project selection list only
when the project count is 1.

Fixes #16420
Revert "Editing user prefs when no project exists triggers error"

This reverts commit 26831ea012ff779155ab7e4a2526ad66f30168ef.

See mantis bug - ALL_PROJECTS should remain in this case
Fixes #16416: Improve first login experience by auto-redirecting to create project page.

If MantisBT is pre-installed, the user lands in My View Page without knowing what to do.
We should handle the "first login" experience in MantisBT itself rather than the installation
and provide a helpful getting started over time. For now, we should start with auto-redirecting
to create project page if user is administrator and there aren't at least 1 project in the database.

The cost of this check is one cheap query on the projects table that returns 0 or 1 entries
which is only run at login of an administrator.
"Fix" #0016431: Numerous "Invalid argument supplied for foreach()" errors when installing with DB script printed to screen
Revert "Revert "Editing user prefs when no project exists triggers error""

This reverts commit 06fc79055388d852e4fedf07068e8115ea45747e.
Don't use '===' when checking return value of config_get()

Follow-up on f2e6550eed6229427392cd995666fe5c000749ea as suggested by
atrol, for consistency use '==' instead like elsewhere in the code.
Fix #15790: url_get() curl user agent is now mantis

Instead of a generic 'curl/version' we now report 'mantisbt/version
php-curl/version'
Fix #15790: with the '/' this time
Localisation updates from http://translatewiki.net.
Localisation updates from http://translatewiki.net.
Remove library/adodb
ADOdb library is now a git submodule

A new 'mantis-1.3' branch was created from upstream's master, which is
currently just before release of V5.19, and will be used to track
MantisBT-specific changes for 1.3.x.

Fixes #14458
Remove library/phpmailer
PHPMailer library is now a git submodule

A new 'mantis' branch was created from upstream's v5.2.6 tag, which will
be used to track MantisBT-specific changes to the library.

Fixes #14458
Revised README.libs after adding git submodules
Updated developers' guide following submodules introduction