Add compatibility with libecal-1.2 and libical-glib

[tintou]

This looks minimal thanks to the previous PRs.
Fixes #404

[decathorpe]

I'm getting some CRITICAL level errors in the logs, but this seems to work fine. Creating and deleting events works, even with locations attached to them. Tested on fedora 31 beta.

(io.elementary.calendar:3278): libical-glib-CRITICAL **: 12:57:58.552: i_cal_geo_get_lat: assertion 'geo != NULL' failed

(io.elementary.calendar:3278): libical-glib-CRITICAL **: 12:57:58.552: i_cal_geo_get_lon: assertion 'geo != NULL' failed

** (io.elementary.calendar:3278): CRITICAL **: 12:57:58.557: maya_services_event_parser_handler_get_parser: assertion 'lang != NULL' failed

** (io.elementary.calendar:3278): CRITICAL **: 12:57:58.557: maya_services_event_parser_get_language: assertion 'self != NULL' failed

** (io.elementary.calendar:3278): CRITICAL **: 12:57:58.557: string_contains: assertion 'self != NULL' failed

(io.elementary.calendar:3278): Gdk-WARNING **: 12:58:01.036: Native Windows taller than 65535 pixels are not supported

(io.elementary.calendar:3278): Gtk-CRITICAL **: 12:58:45.781: gtk_text_buffer_set_text: assertion 'text != NULL' failed

** (io.elementary.calendar:3278): CRITICAL **: 12:58:45.790: maya_services_event_parser_handler_get_parser: assertion 'lang != NULL' failed

** (io.elementary.calendar:3278): CRITICAL **: 12:58:45.790: maya_services_event_parser_get_language: assertion 'self != NULL' failed

** (io.elementary.calendar:3278): CRITICAL **: 12:58:45.790: string_contains: assertion 'self != NULL' failed

(io.elementary.calendar:3278): Gtk-CRITICAL **: 12:58:54.034: gtk_text_buffer_set_text: assertion 'text != NULL' failed

** (io.elementary.calendar:3278): CRITICAL **: 12:58:54.042: maya_services_event_parser_handler_get_parser: assertion 'lang != NULL' failed

** (io.elementary.calendar:3278): CRITICAL **: 12:58:54.042: maya_services_event_parser_get_language: assertion 'self != NULL' failed

** (io.elementary.calendar:3278): CRITICAL **: 12:58:54.042: string_contains: assertion 'self != NULL' failed

[worldofpeace]

Thanks for the prompt integration ❤️