Add a getter/setter for torrent announce URLs as text that can be copied
and pasted: one URL per line, with a blank line between tiers.
C API: tr_torrentGetTrackerList() and tr_torrentSetTrackerList()
RPC APi: `trackerList` in `torrent-get` and `torrent-set`.
This deprecates `trackerAdd`, `trackerRemove`, and `trackerEdit`
from the RPC API.
* refactor: prefer constexpr over enum for GUI_PAD values
* refactor: prefer constexpr over enum for PrefsDialog values
* refactor: prefer constexpr over enum for StatsDialog values
* refactor: use enum class for GtrUnicode types
* refactor: prefer constexpr over enum for BT peer msg codes
* refactor: use enum class for TrMakemetaResult
* refactor: prefer constexpr over enum for BT metadata message types
* refactor: use enum class for AwaitingBt
* refactor: use enum class for EncryptionPreference
* refactor: use enum class for TrFormat in rpcimpl
* refactor: prefer constexpr over enum for QApp intervals
* refactor: prefer constexpr over enum for tr_resume bitfields
* refactor: prefer constexpr over enum for Qt/TrFileModel bitfields
* refactor: remove obsolete TODO comment in announce-list
* refactor: include <memory> when using shared_ptr or unique_ptr
* refactor: include <cstdio> iff we use it
* refactor: include <cstring> iff we use it
* refactor: include <cstdlib> iff we use it
* refactor: include <string_view> or <string> iff we use it
* refactor: include <array> iff we use it
* refactor: include <ctime> iff we use it
* refactor: include <cctype> iff we use it
* refactor: misc #include cleanups in libtransmission
