Switch away from using nevow

[habnabit]

As part of the effort of porting to python 3, moving the web code away from nevow is the simplest option, since nevow won't be updated (and the code is using old parts of nevow anyway) but twisted.web is already compatible with python 3. twisted.web.template already does most of what the templates used in nevow in the first place.

Since nevow and twisted.web interoperate enough, this port can be done piecemeal at the granularity of one template per ticket/PR.

• #3245: allmydata.web.introweb
• #3246: allmydata.web.info
• #3247: allmydata.web.storage
• #3252: allmydata.web.directory
  • #3263: manifest (part of "directory")
  • #3381: DeepSizeResults
• #3254: allmydata.web.status
  • #3287: allmydata.web.status.UploadStatusPage
  • #3288: allmydata.web.status.DownloadStatusPage
  • #3289: allmydata.web.status.PublishStatusPage
  • #3290: allmydata.web.status.RetrieveStatusPage
  • #3291: allmydata.web.status.MapupdateStatusPage
  • #3292: allmydata.web.status.Statistics
  • #3293: allmydata.web.status.HelperStatus
• #3257: allmydata.web.root.URIHandler
• #3305: allmydata.web.root.Root
• #3432: Replace Nevow imports in tests with Twisted's equivalents
  • allmydata.test.test_checker
  • allmydata.test.web.test_storage_web
  • allmydata.test.web.test_token
  • allmydata.test.web.test_web
• #3392: allmydata.test.common_web.WebRenderingMixin
• #3393: allmydata.web._nevow_106
• allmydata.web.operations
  • #3313: allmydata.web.operations.OphandleTable
  • #3315: allmydata.web.operations.ReloadMixin
• allmydata.web.common
  • #3382: allmydata.web.common.MultiFormatPage
  • #3436: Remove unused web.common.getxmlfile()
• #3316: allmydata.web.check_results
• import of nevow.url
  • #3314: nevow.url in in web.filenode
  • nevow.url in web.operations
  • nevow.url in web.unlinked
• #3433: allmydata.webish
• #3434: static/tahoe.py
• #3435: misc/build_helpers/show-tool-versions.py
• #3420: Twisted web Resources should do "return ErrorPage" instead of "raise WebError"
• #3428: twisted.web.resource.Resource subclasses should not return Deferreds

These were formerly part of the web UI, but they are no longer in use, and so probably not relevant to porting:

• misc/operations_helpers/provisioning/provisioning.py
• misc/operations_helpers/provisioning/run.py
• misc/operations_helpers/provisioning/test_provisioning.py
• misc/operations_helpers/provisioning/web_reliability.py

[habnabit]

• #3245: allmydata.web.introweb
• #3246: allmydata.web.info

[exarkun]

All of the work to actually stop depending on Nevow was completed a while ago. There is one more open ticket linked from this one but it is an optional improvement. Tahoe-LAFS does not actually use or depend on Nevow anymore.