INSTALL: mention that root access may be needed for install

Because not everyone building Wesnoth knows how to use their OS.
Only update button states if zoom level changed.
Refactored the editor's select tool into its own files.
vc project update
cb project update
Updated XCode projfile (added editor selection action files)
Goto MAI: Ensure that persistent data always are in WML table format

This also means that keys cannot contain certain symbols and, as a
result, potentially user-provided strings need to be stored in the
values, not keys.  This fixes bug #20924 about the Goto MAI corrupting
saves.
Flip the default value for shroud_clearer::clear_unit()'s instant parameter.

The original (from r56169) default of false was not working as well as I
thought it was. So now the default is true, and the places where false
was providing a benefit explicitly pass false.
Fixes bug #20602.
Amends the fix to bug #20324.