Stream CrossPointWebServer data over JSON APIs (#97)

## Summary

* HTML files are now static, streamed directly to the client without
modification
* For any dynamic values, load via JSON APIs
* For files page, we stream the JSON content as we scan the directory to
avoid holding onto too much data

## Additional details

* We were previously building up a very large string all generated on
the X4 directly, we should be leveraging the browser
* Fixes https://github.com/daveallie/crosspoint-reader/issues/94

platformio.ini

@@ -9,7 +9,7 @@ framework = arduino
 monitor_speed = 115200
 upload_speed = 921600
 check_tool = cppcheck
-check_flags = --enable=all --suppress=missingIncludeSystem --suppress=unusedFunction --suppress=unmatchedSuppression --inline-suppr
+check_flags = --enable=all --suppress=missingIncludeSystem --suppress=unusedFunction --suppress=unmatchedSuppression --suppress=*:*/.pio/* --inline-suppr
 check_skip_packages = yes
 
 board_upload.flash_size = 16MB
@@ -39,6 +39,7 @@ lib_deps =
   BatteryMonitor=symlink://open-x4-sdk/libs/hardware/BatteryMonitor
   InputManager=symlink://open-x4-sdk/libs/hardware/InputManager
   EInkDisplay=symlink://open-x4-sdk/libs/display/EInkDisplay
+  ArduinoJson @ 7.4.2
 
 [env:default]
 extends = base