[Wallet] Watch-only fixes
qt: add network-specific style object

Mainly cleanups: Gets rid of isTestNet everywhere, by keeping track
of network-specific theming in a central place.

Also makes GUI no longer dependent on the network ID enumeration, which
alleviates concerns about #4802.
Move checkpoint data selection to chainparams
Add fTestnetToBeDeprecatedFieldRPC to CChainParams
Remove CChainParams::NetworkID()
Merge pull request #4802

6fd546d Remove CChainParams::NetworkID() (jtimon)
cc97210 Add fTestnetToBeDeprecatedFieldRPC to CChainParams (jtimon)
e11712d Move checkpoint data selection to chainparams (jtimon)
6de50c3 qt: add network-specific style object (Wladimir J. van der Laan)
build: fix dynamic boost check when --with-boost= is used
build: fix qt test build when libprotobuf is in a non-standard path
Merge pull request #5073

d5fd094 build: fix qt test build when libprotobuf is in a non-standard path (Cory Fields)
a7d1f03 build: fix dynamic boost check when --with-boost= is used (Cory Fields)
Merge pull request #4937

ccca27a [Wallet] Watch-only fixes (Cozz Lovan)
Typo in test
Merge pull request #5080

e21b2e0 Typo in test (Luke)