add BlockDevices examples

[maciejbocianski]

Move examples:
https://os.mbed.com/teams/mbed_example/code/HeapBlockDevice_ex_1/
https://os.mbed.com/teams/mbed_example/code/ChainingBlockDevice_ex_1/
https://os.mbed.com/teams/mbed_example/code/ChainingBlockDevice_ex_2/
to this repo

Update examples:
https://os.mbed.com/teams/mbed_example/code/MBRBlockDevice_ex_1/
https://os.mbed.com/teams/mbed_example/code/MBRBlockDevice_ex_2/
https://os.mbed.com/teams/mbed_example/code/ProfilingBlockDevice_ex_1/
https://os.mbed.com/teams/mbed_example/code/SlicingBlockDevice_ex_1/

Update example code to latest API's

Docs update PR: ARMmbed/mbed-os-5-docs#1273

[jamesbeyond]

@maciejbocianski, I clicked on the update branch button, seems it created a commit on your branch. I didn't found how I can revert what I did in Github. Could you drop what I did and rebase this PR? so we can keep the master a bit cleaner.

[AnotherButler]

Thanks for the PR 👍