chore(release): bump version to 0.3.0

Bump plugin version from 0.2.8 to 0.3.0 in VERSION, manifest.json,
__init__.py and core/plugin_base.py for the 0.3.0 release (postpone
invalidation safety + Server status column).

bal/manifest.json

@@ -1,7 +1,7 @@
 {
     "name": "bal",
     "fullname": "Bitcoin After Life",
-    "version": "0.2.8",
+    "version": "0.3.0",
     "description": "Provides free and decentralized Bitcoin inheritance support. Build time-locked 'will' transactions that transfer funds to your heirs if you stop refreshing them (dead-man's switch), optionally relayed by will-executor servers.",
     "author": "Svatantrya",
     "licence": "MIT",