Catch loading issues (#255)

* various loading improvements to avoid pages getting 'stuck' + load state tracking
- add PageState object, store loadstate (0 to 4) as well as other per-page-state properties on defined object.
- set loadState to 0 (failed) by default
- set loadState to 1 (content-loaded) on 'domcontentloaded' event
- if page.goto() finishes, set to loadState to 2 'full-page-load'. 
- if page.goto() times out, if no domcontentloaded either, fail immediately. if domcontentloaded reached, extract links, but don't run behaviors
- page considered 'finished' if it got to at least loadState 2 'full-pageload', even if behaviors timed out
- pages: log 'loadState' as part of pages.jsonl
- improve frame detection: detect if frame actually not from a frame tag (eg. OBJECT) tag, and skip as well
- screencaster: try screencasting every frame for now instead of every other frame, for smoother screencasting
- deps: behaviors: bump to browsertrix-behaviors 0.5.0-beta.0 release (includes autoscroll improvements)
- workers ids: just use 0, 1, ... n-1 worker indexes, send numeric index as part of screencast messages
- worker: only keeps track of crash state to recreate page, decouple crash and page failed/succeeded state
- screencaster: allow reusing caster slots with fixed ids
- interrupt timedCrawlPage() wait if 'crash' event happens
- crawler: pageFinished() callback when page finishes
- worker: add workerIdle callback, call screencaster.stopById() and send 'close' message when worker is empty

yarn.lock

@@ -1079,10 +1079,10 @@ browserslist@^4.21.3:
     node-releases "^2.0.6"
     update-browserslist-db "^1.0.9"
 
-browsertrix-behaviors@^0.4.2:
-  version "0.4.2"
-  resolved "https://registry.yarnpkg.com/browsertrix-behaviors/-/browsertrix-behaviors-0.4.2.tgz#830f4e37ddebf10dd923237dfd75c734d5d211e9"
-  integrity sha512-5w6kPL3NB/BkmEGxWt3NT3iddAaSzMR1TtDPS7b66fM9kkhpCjCv/R/zR951jWDIeV3flJFBOy09uI5o8asPqg==
+browsertrix-behaviors@^0.5.0-beta.0:
+  version "0.5.0-beta.0"
+  resolved "https://registry.yarnpkg.com/browsertrix-behaviors/-/browsertrix-behaviors-0.5.0-beta.0.tgz#d1a7c35cda31d740a374df1e833f36bd1890768d"
+  integrity sha512-RQMQlbV4OBAzYyhTI7imoem8p4MTj2XSDzlIZvA5sC5U89OMnJ0VM5KBAJzET3PUJkQlUQEOTiXtnsnodHXTUQ==
 
 bser@2.1.1:
   version "2.1.1"