libplist: Update to version 2.7.0

libplist: Update to version 2.7.0

- Update from version 2.4.0 to 2.7.0
- Update of rootfile
- Changelog
    2.7.0
	- Changes:
	  * Add plist_new_unix_date, plist_get_unix_date_val, plist_set_unix_date_val
	    functions that work with int64_t values representing a UNIX timestamp
	    instead of using the 'MAC epoch'.
	    These new functions should be used instead of plist_new_date,
	    plist_get_date_val, and plist_set_date_val, which are now marked deprecated
	    and might be removed in a future version of libplist.
	  * Allow building the library without tool(s)
	  * Switch to more generic global initializer method
	  * json: Allow e+/E+ in exponent as per RFC 8259
	  * C++: Add more convenience functions to the interface
	  * C++: Add more type variants to different constructors and operators
	- Bugfixes:
	  * Fix segmentation fault when calling plist_sort() on an empty dictionary
	  * Fix compilation on MSVC
	  * C++: Fix bug in internal helper function of Array class
	  * C++: Fix String::GetValue memory leaking and support assignment of const
	    char*
    2.6.0
	- Changes:
	  * Revert back API change around PLIST_DATA to use char* again
    2.5.0
	- Changes:
	  * Change API around PLIST_DATA to use uint8_t* instead of char*
	  * Add PLIST_DICT helper functions for different operations
	  * Require Cython 3.0 for python bindings

Signed-off-by: Adolf Belka <adolf.belka@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>