merge changes from monero: coverity fixes (PR #4617)

[bleepster]

Merging the following commits:

• blockchain_db: initialize m_hardfork in ctor just in case (blockchain_db: initialize m_hardfork in ctor just in case)
• wallet2: initialize some scalar fields in ctor where appropriate (32123789129372f1a4cb46a8aa289843e15a4b37)
• account: init creation timestamp to 0 (7cc39845be1cfa9286dec589d4f1c94381b140d9)
• rpc: remove unused ctors (bfa2dce171e2a04096c07f204037ccd13dc2fae6)
• rpc: init m_rpc_version in Message ctor (3ffbec1556f8817cb014fcea83bccc41747cfcf5)

See individual commit messages for details.