docs(bal): rewrite CHECK ALIVE help text (DATA/RAW modes) + fix two typos (v0.3.8)

Rewrite the CHECK ALIVE help popup (ThresholdTimeWidget.help_text) to explain
both modes, keeping the <b>CHECK ALIVE</b> title bold:
- DATA mode: set the check-alive date; on wallet open, if the date has passed
  the plugin asks whether to postpone the inheritance.
- RAW mode: when less than this time is missing, ask to invalidate; failing to
  invalidate delivers the transactions to the heirs; kept the d/y suffix help.

Fix two typos within this help text: 'less then' -> 'less than',
'currrent' -> 'current'.

Bump version to 0.3.8 across the four version files. CHANGELOG entry #14.

bal/core/plugin_base.py

@@ -91,7 +91,7 @@ class BalPlugin(BasePlugin):
     """
 
     _version = None
-    __version__ = "0.3.7"  # AUTOMATICALLY GENERATED DO NOT EDIT
+    __version__ = "0.3.8"  # AUTOMATICALLY GENERATED DO NOT EDIT
 
     # Command used to open an .ics calendar file, per operating system.
     default_app = {