Add an uninstaller for Linuxes

Makefile

@@ -112,3 +112,9 @@ install:
 	cp -vr build/profile /var/lib/i2pbrowser/profile
 	cp -vr build/app-profile /var/lib/i2pbrowser/app-profile
 
+uninstall:
+	rm -rfv /etc/i2pbrowser \
+		/var/lib/i2pbrowser \
+		/etc/i2pbrowser/i2pbrowserrc \
+		/usr/local/bin/i2pbrowser \
+		/usr/local/bin/i2pconfig

src/unix/i2pbrowser.sh

@@ -14,6 +14,7 @@ if [ ! -d "$BROWSING_PROFILE" ]; then
 fi
 
 if [ ! -f "$BROWSING_PROFILE/user.js" ]; then
+  echo "user.js not present in $BROWSING_PROFILE, this is not a Firefox profile"
   exit 1
 fi
 

src/unix/i2pconfig.sh

@@ -14,6 +14,7 @@ if [ ! -d "$CONFIGURING_PROFILE" ]; then
 fi
 
 if [ ! -f "$CONFIGURING_PROFILE/user.js" ]; then
+  echo "user.js not present in $CONFIGURING_PROFILE, this is not a Firefox profile"
   exit 1
 fi