Fix keyboard related issues on Ubuntu 18.04

Fix keyboard related issues on Ubuntu 18.04

On Ubuntu 18.04, the keyboard was not properly handled in PROX
For instance, many keys pressed were silently discarded.

The issue is related to a change in histedit/libedit version.
Recent libedit have (silently) changed the prototype of the get_char function
passed in el_set(el, EL_GETCFN, get_char), with some input parameters
changing from char to wchar_t.
As PROX used the old prototype (char based), this resulted in some
uninitialized field (= garbage) in the wchar_t, causing libedit to discard
the character.

PROX now uses different get_char prototypes, depending of the libedit version
being used.

If PROX was already compiled and a the OS is updated (e.g. from Ubuntu 16.04
to Ubuntu 18.04), this will require a 'make clean'.

Change-Id: Icb0e555a21e13cdaf98172bad17f2f838fb7bc3a
Signed-off-by: Xavier Simonart <xavier.simonart@intel.com>