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/theme/common/landscape.xml b/gui/theme/common/landscape.xml
index 3039252..0b8860e 100644
--- a/gui/theme/common/landscape.xml
+++ b/gui/theme/common/landscape.xml
@@ -1676,8 +1676,8 @@
 
 			<checkbox>
 				<placement x="%col1_x_right%" y="%row7a_y%"/>
-				<text>{@skip_md5_backup_chk=Skip MD5 generation during backup}</text>
-				<data variable="tw_skip_md5_generate"/>
+				<text>{@skip_digest_backup_chk=Skip Digest generation during backup}</text>
+				<data variable="tw_skip_digest_generate"/>
 			</checkbox>
 
 			<checkbox>
@@ -2272,8 +2272,8 @@
 
 			<checkbox>
 				<placement x="%col1_x_right%" y="%row6_y%"/>
-				<text>{@restore_enable_md5_chk=Enable MD5 Verification of Backup Files}</text>
-				<data variable="tw_skip_md5_check"/>
+				<text>{@restore_enable_digest_chk=Enable Digest Verification of Backup Files}</text>
+				<data variable="tw_skip_digest_check"/>
 			</checkbox>
 
 			<button style="main_button_half_width">
@@ -2866,11 +2866,11 @@
 				<listitem name="{@disable_backup_space_chk=Disable free space check before backup}">
 					<data variable="tw_disable_free_space"/>
 				</listitem>
-				<listitem name="{@skip_md5_backup_chk=Skip MD5 generation during backup}">
-					<data variable="tw_skip_md5_generate"/>
+				<listitem name="{@skip_digest_backup_chk=Skip Digest generation during backup}">
+					<data variable="tw_skip_digest_generate"/>
 				</listitem>
-				<listitem name="{@restore_enable_md5_chk=Enable MD5 verification of backup files}">
-					<data variable="tw_skip_md5_check"/>
+				<listitem name="{@restore_enable_digest_chk=Enable Digest verification of backup files}">
+					<data variable="tw_skip_digest_check"/>
 				</listitem>
 				<listitem name="{@use24clock_chk=Use 24-hour clock}">
 					<data variable="tw_military_time"/>