Add BLE client

[beegee-tokyo]

This adds a BLE client that can replace the web socket / WiFi server client.

Remarks:

• Larger app partition is required as BLE occupies too much program memory to fit into default app partition size
• Exclusive usage of either BLE or WiFi! On an ESP32 Wroom there is not enough heap available to run both in parallel. Solution would be to use ESP32 Wrover with at least 4MB PSRAM. On Wrover modules both WiFi and BLE are using PSRAM automatically.
• main.ino is patched to initialize either WiFi or BLE client depending on the compiler flag USE_BLE set or not.

  Android app

  Android app source code can be found in my repo disaster-radio-android. I will publish it on Google Play if you agree to it.

  What does not work yet?

• WelcomeMessage()
  • Could not get WelcomeMessage class to work as it sends the welcome message immediately even when no BLE client is connected. Still searching for a workaround
• HistoryReplay()
  • History is not working as well. Not sure how to implement it. Help needed!

[beegee-tokyo]

ESP32 Arduino has already a BLEClient class, so there is a name conflict. That's why I called it different. I think even naming the files the same as in ESP32 Arduino is not a good solution and can lead to confusion.

I can make the void startServer(void (*callback)(BleDrClient *)); static, I just saw no requirement for it.

[beegee-tokyo]

Renaming of files and classes done to
a) match naming consistency b) avoid problems with ESP32 BLEClient library

Made startServer() static.

[paidforby]

Really great stuff. I finally had some time to test this. Works great. The only change I am making is to the platformio.ini to keep it the default/recommended settings (i.e. ttgo v2, /dev/ttyUSB0, wifi enabled), but include your settings as commented out options.

It also appears that you overlooked one use of ble_client here. I just wrapped the if (client == NULL) in an #ifdef USE_BLE.

I'm going to go ahead and merge this into master is if that is OK with you, @beegee-tokyo. Maybe we should create a fork where BLE is the default for convenience's sake? Not sure the best way to manage these minor differences. Ideally, we'd be able to swap between them more dynamically.

Thanks for the awesome contribution! I will be making some changes to the way the clients communicate related to #48 so be aware that the android app maybe need to be updated once that issue is resolved.

[beegee-tokyo]

Great. Thanks for merging.

I didn't go into the dynamic switch between WiFi and BLE, because I know you were working on the way data is transferred between clients and servers. So for me it is ok to have it in a separate branch/fork for now.

Once the #48 is finished, let me know, I will adapt the Android app where necessary.

For the overlooked ble_client use, that is actually something strange. Sometimes when the Welcome Class is initiated, the client value was NULL instead of being the BLE client. I couldn't find out why and where it happens, it seems to be a kind of runtime problem.