[sb2] Use $SBOX_HOME_DIR instead of $HOME to save target configs

If $SBOX_HOME_DIR is not set, default to $HOME.

SBOX_HOME_DIR can be given on the command line with the new option -H
with sb2, sb2-init and some other scripts or it can be read from the
environment.

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>
[sb2] Add sb2-common to be sourced into scripts

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>
[sb2] Use sb2-common to set SBOX_HOME_DIR

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>
[sb2] Minor fixes to main makefile and packaging

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>
[sb2-config] Add -V and -Q options to sb2-config

Use the -V option with -l or -f to highlight the default
sb2 target with a '*'

Use sb2-config -Q to print out the sbox home directory

Signed-off-by: Juha Kallioinen <juha.kallioinen@jollamobile.com>