Add Liberapay alongside Ko-fi for donations (#430)

Adds Liberapay as a second donation option next to Ko-fi.

- Settings: "Support development" now opens a full-screen picker with Ko-fi (one-off tips) and Liberapay (recurring donations) instead of linking straight to Ko-fi.
- README: Liberapay badge next to the Ko-fi badge, plus a short Support section.

No issue for this one.

Co-authored-by: Jean-Luc Makiola <business@jeanlucmakiola.de>
Reviewed-on: https://codeberg.org/jlmakiola/calendula/pulls/430

app/src/main/res/values/strings.xml

@@ -681,6 +681,10 @@
     <string name="settings_licences_subtitle">The projects Calendula is built on</string>
     <string name="settings_about_privacy">Privacy policy</string>
     <string name="settings_about_support">Support development</string>
+    <string name="settings_support_kofi">Ko-fi</string>
+    <string name="settings_support_kofi_hint">One-off tips</string>
+    <string name="settings_support_liberapay">Liberapay</string>
+    <string name="settings_support_liberapay_hint">Recurring donations</string>
     <string name="settings_about_version">Version %1$s</string>
     <string name="settings_about_logo_desc">Calendula app icon</string>
     <string name="settings_report_problem">Report a problem</string>
@@ -834,7 +838,8 @@
     <string name="about_source_url" translatable="false">https://codeberg.org/jlmakiola/calendula</string>
     <string name="about_license_url" translatable="false">https://codeberg.org/jlmakiola/calendula/src/branch/main/LICENSE</string>
     <string name="about_privacy_url" translatable="false">https://jeanlucmakiola.de/calendula/privacy</string>
-    <string name="about_support_url" translatable="false">https://ko-fi.com/jeanlucmakiola</string>
+    <string name="about_support_kofi_url" translatable="false">https://ko-fi.com/jeanlucmakiola</string>
+    <string name="about_support_liberapay_url" translatable="false">https://liberapay.com/Jean-Luc_Makiola/donate</string>
     <string name="about_translate_url" translatable="false">https://weblate.dev.jeanlucmakiola.de/engage/calendula/</string>
 
     <!-- Crash reporting: a captured report the user can submit, by hand, as a