twrpDigest refactor

This patch is to refactor twrpDigest using polymorphism
and inheritance to use the same call patterns for creating and
reading a digest. Now a library.
Use SHA2 from libcrypto. SHA2 is default if device has libcrypto.

Change string MD5 everywhere to use digest or Digest instead. Updated
string tags to digest. Translation will be required.

Switch out digest code into a driver class from partitionmanager.

SHA2 is better for digest creation due to decreased collision space
compared to MD5 and SHA1.

See https://en.wikipedia.org/wiki/SHA-2

Change-Id: I74b5546789990b12aa4ce2e389d25f80a3fe213f
diff --git a/gui/pages.cpp b/gui/pages.cpp
index bf6c692..b901526 100644
--- a/gui/pages.cpp
+++ b/gui/pages.cpp
@@ -52,7 +52,7 @@
 #include "blanktimer.hpp"
 
 // version 2 requires theme to handle power button as action togglebacklight
-#define TW_THEME_VERSION 2
+#define TW_THEME_VERSION 3
 
 #define TW_THEME_VER_ERR -2