Reduce the code a reviewer must read #336

CipherStick's pitch is that it adds little code on top of Tails and
Bitcoin Core. That only holds while the code stays small, so this tracks
cutting it.

Today on master (af1864d, cloc code lines): 1,009 lines of bash in 17
scripts (1,631 with comments and blanks). The largest are install-core
(192), persistent-setup (136), b (122), cryostick (98) and open-codex32
(98).

python-codex32, which Bails pins, is the larger share: about 6,700 lines
for the library plus GUI. Not shipping its CLI and dropping
insertion/deletion correction would take it to about 4,250.

Open PRs that shrink Bails' bash (net code-file lines vs master):

• core: remove obsolete IBD backup watcher #286 remove obsolete IBD backup watcher: -58
• setup: simplify completion UI #282 simplify completion UI: -14
• ui: quiet chainstate preload status #283 quiet chainstate preload status: -7
• menu: Hide unfinished backup actions #219 hide unfinished backup actions: -6

Open PRs that grow it: #311 (+254, replaces the autostarts and adds
the core-config, core-dbcache and core-prune helpers), #285 (+70) and
#276 (+19).

Ideas to look at:

• Leave unfinished menu items (Clone, Backup) out until they exist,
  rather than shipping stubs.
• Use Tails and Debian interfaces in place of local code (see the
  maintainability policy in docs/developer-notes.md).
• Keep each script under 100 lines, per the review rules on core: pass catch-up dbcache on the command line #311.