Make source changes needed for certora verification

We need to change two private functions to internal so we can harness them
and verify properties of these functions.
See related PR that builds on this change: #256

src/EVault/modules/Liquidation.sol

@@ -62,7 +62,7 @@ abstract contract LiquidationModule is ILiquidation, BalanceUtils, LiquidityUtil
         address violator,
         address collateral,
         uint256 desiredRepay
-    ) private view returns (LiquidationCache memory liqCache) {
+    ) internal view returns (LiquidationCache memory liqCache) {
         // Init cache
 
         liqCache.liquidator = liquidator;

src/EVault/shared/Cache.sol

@@ -39,7 +39,7 @@ contract Cache is Storage, Errors {
     // Takes a VaultCache struct, overwrites it with VaultStorage data and, if time has passed since VaultStorage
     // was last updated, updates VaultStorage.
     // Returns a boolean if the cache is different from storage. VaultCache param is updated to this block.
-    function initVaultCache(VaultCache memory vaultCache) private view returns (bool dirty) {
+    function initVaultCache(VaultCache memory vaultCache) internal view returns (bool dirty) {
         dirty = false;
 
         // Proxy metadata