fixes for PHP 7.3. Tested on running system.

[leonhedding]

I was unaware that the code did not work with PHP 7.3. The rest of FreePBX 15.x was running fine with PHP 7.3 so I went with that. I then found that this code did not work. I needed to fix various warnings generated with deprecated syntax. No new features.

[lgaetz]

I know this PR was intended for FreePBX 15 with PHP 7.3, but wanted to point out, in case others are hoping, that it will not work for FreePBX 16 with php 7.4. Install fails with

# fwconsole ma install endpointman
Updating tables endpointman_brand_list, endpointman_custom_configs, endpointman_global_vars, endpointman_line_list, endpointman_mac_list, endpointman_model_list, endpointman_oui_list, endpointman_product_list, endpointman_template_list, endpointman_custom_configs...Done

In json.class.php line 234:

  Array and string offset access syntax with curly braces is deprecated

[ronindesign]

Unfortunate to see this hasn't been merged yet... Also, any chance to get support for FreePBX v16 (or even v17) and PHP 7.4? I'm running into the same issue @lgaetz mentioned above on FreePBX v16, PHP 7.4

In json.class.php line 234:

  Array and string offset access syntax with curly braces is deprecated