exceptions: Make Tlv::Error a base class for all packet-processing exceptions

This commit also includes a number of code style fixes.

Change-Id: I44f83915e733b43d5f43b4266902c8262e928d91
Refs: #1528
diff --git a/src/security/validator-regex.cpp b/src/security/validator-regex.cpp
index 1eea45e..e9558c6 100644
--- a/src/security/validator-regex.cpp
+++ b/src/security/validator-regex.cpp
@@ -152,13 +152,13 @@
                   return;
                 }
             }
-          catch (const SignatureSha256WithRsa::Error& e)
+          catch (SignatureSha256WithRsa::Error& e)
             {
               return onValidationFailed(data.shared_from_this(),
                                         "Not SignatureSha256WithRsa signature: " +
                                         data.getName().toUri());
             }
-          catch (const KeyLocator::Error& e)
+          catch (KeyLocator::Error& e)
             {
               return onValidationFailed(data.shared_from_this(),
                                         "Key Locator is not a name: " +