Add Network related examples

[mprse]

No description provided.

[mprse]

DATAFLASHBLOCKDEVICE example fails because it requires DATAFLASH to be added to K64F components list. This is done via mbed_app.json configuration file which is added to the example directory.
The problem is that mbed test probably ignores this file.

[mprse]

Solved CI issue. This one is ready to go.

[jamesbeyond]

Solved CI issue. This one is ready to go.

Hey @mprse, thanks for the changes, but sorry I might need to ask you split this PR into 3. because they contain examples of several teams. one PR would be difficult for people to review, and slow down the merge process.
So I suggested split them into 3:

• NFC related ->PAN team
• Storage -> STORAGE team
• Network and Cellular -> Cellular team

[mprse]

@jamesbeyond Split this one as requested:
NFC related ->PAN team (PR #87)
Storage -> STORAGE team (PR #86)
Network and Cellular -> Cellular team (this one)

I also added missing headers.

[jamesbeyond]

LGTM

[jamesbeyond]

Hi @AnttiKauppila,
could you have a look, see if you happy about those snippets examples, they been moved from https://github.com/ARMmbed/mbed-os-5-docs/blob/development/docs/api/networksocket/CellularNonIPSocket.md#cellularnonipsocket-example
to here

[mprse]

Maybe I should change APIs_networksocket/... to APIs_Network/.... This would be more generic and suitable also for examples like:
https://os.mbed.com/teams/mbed_example/code/TCPSocket_Example/file/50f1485931f1/main.cpp/

[jamesbeyond]

Maybe I should change APIs_networksocket/... to APIs_Network/.... This would be more generic and suitable also for examples like:
https://os.mbed.com/teams/mbed_example/code/TCPSocket_Example/file/50f1485931f1/main.cpp/

Maybe APIs_NetworkSocket/... with little changes on the caps to match all others? in the documents, it is under NetworkSocket page :
https://os.mbed.com/docs/mbed-os/v5.15/apis/non-ip-cellular-socket.html

[mprse]

Rebased and updated directory name as suggested.