write characterstic limited to 20 bytes

[vladtepesch]

Describe the bug
write characterstic limited to 20 bytes/text characters

Expected behavior
limit should be the devices MTU

To Reproduce
Try to write to a charactersitic, chose text, enter long text

Screenshots

Your environment
Please describe the environment you are using:

1. What is your operating system: Windows
2. Where did you download/bought the application: Github
3. The version of the application you are running: 0.15

Additional context
...

[thekief]

Sorry to broaden the context but chunking would also be incredibly useful in this context.

There are a few instances, where it would be quite useful to test, if an application behaves correctly with smaller packets.