Some questions:

• The format is consistent in these changes, but it's not consistent through the code base. Should the format be <datatype>& <identifier> or <datatype> &<identifier>?
• without an identifier; some places in the code are by reference, some by value
  test\alert_tests\cpp Line 96: catch (std::exception) { }
rpc\rawtransaction.cpp Line 620: } catch (const std::exception&) {
• While we're at it; should we define the catches to be const?
• Should this be expanded to include the test modules?
  test\benchmark_zerocoin.cpp
test\libzerocoin_tests.cpp
test\alert_tests.cpp

Addressing your questions:

• Well that's my bad because https://github.com/PIVX-Project/PIVX/blob/master/doc/developer-notes.md#coding-style-c specifies that the desired format is <datatype>& <identifier>. I fixed it.
• I fixed the warnings thrown by my compiler. Here is an explanation about the reasons behind this warning: https://blog.knatten.org/2010/04/02/always-catch-exceptions-by-reference/ We can assume that the places such as test\alert_tests\cpp Line 96: catch (std::exception) { } don't throw a warning because the exception is not used, thus we don't really care if it's missing some specific methods or data. I fixed it anyway so it can be used safely in the future.
• Indeed, adding const to exceptions catching is not that important of a change but it's always good to have. So I added it too.
• Of course test modules must be included. And they were. Only alert_tests.cpp wasn't changed because as I said above it didn't throw a warning. That's done too now.

• Well that's my bad because https://github.com/PIVX-Project/PIVX/blob/master/doc/developer-notes.md#coding-style-c specifies that the desired format is <datatype>& <identifier>. I fixed it.

Good reference; I will check it out so I can be more authoritative in the future ;)

Needs rebase

Rebased

Doesn't compile. There's some conflict leftover in masternode.cpp since #1001 has been merged.

Indeed. Should be good now.