mate-desktop 1.26.0 release

Changes since the last release: v1.25.0...v1.26.0

mate-desktop 1.26.0

• Translations update
• Replace the obsolete API in mate-colorsel.c file
• Fix compilation warning
• update copyright to 2021
• travis-ci: use ubuntu focal as host system
• MATE About: Fix off-by-one error, display yerba mate comment
• travis: disable travis builds for ubuntu
• Remove shadow warnings [-Wshadow]
• mate-about: Use the macro _(String) instead of the macro gettext(Msgid)
• Drop local macro mate_gettext(package, locale, codeset)
• Remove warning -Wbad-function-cast
• g_settings_get_string always returns a newly-allocated string
• build: set GETTEXT_PACKAGE=AC_PACKAGE_NAME
• tx: update resource
• mate-color-select: Do not use deprecated gtk_button_new_from_stock
• update issue template
• Remove USE_MATE2_MACROS from autogen.sh (legacy)
• travis CI: use rolling tag for ubuntu docker image
• travis CI: fix build issue of gtk-doc module