libtracker-data: remove unneeded fallback methods to use glib as unicode support

We already require either libunistring or libicu, so the glib-based fallback
methods will actually never be used.
libtracker-data: new 'tracker:normalize' method

https://bugzilla.gnome.org/show_bug.cgi?id=722254

This method allows normalizing the strings used in SPARQL queries. It expects
two arguments: First, the string to be normalized, and second, one of "nfc",
"nfd", "nfkc" or "nfkd" specifying the type of normalization to apply to the
string.

Example:

1) First, insert a new element which has accents in the nie:title. In the
example we insert the word 'école' which in UTF-8 NFC looks like
"0xC3 0xA9 0x63 0x6F 0x6C 0x65":

    $ tracker-sparql -u -q "
        INSERT { <abc> a         nie:InformationElement .
                 <abc> nie:title 'école' }"

2) Second, get hexdump of querying nie:title, we should get the original string
in UTF-8 and NFC normalization:

    $ tracker-sparql -q "
        SELECT ?title
        WHERE { <abc> nie:title ?title }" | hexdump
    0000000 6552 7573 746c 3a73 200a c320 63a9 6c6f
    0000010 0a65 000a
    0000013

3) Third, now apply explicitly NFC normalization, we should get the same output:

    $ tracker-sparql -q "
        SELECT tracker:normalize(?title,'nfc')
        WHERE { <abc> nie:title ?title }" | hexdump
    0000000 6552 7573 746c 3a73 200a c320 63a9 6c6f
    0000010 0a65 000a
    0000013

4) Last, apply a NFD decomposition, the expected decomposed string should look
like "0×65 0xCC 0x81 0×63 0x6F 0x6C 0×65":

    $ tracker-sparql -q "
        SELECT tracker:normalize(?title,'nfkd')
        WHERE { <abc> nie:title ?title }" | hexdump
    0000000 6552 7573 746c 3a73 200a 6520 81cc 6f63
    0000010 656c 0a0a
    0000014
libtracker-data: new 'tracker:unaccent' method

https://bugzilla.gnome.org/show_bug.cgi?id=722254

This method allows removing combining diacritical marks (accents) from strings
used in SPARQL queries. It expects a single argument, the string to be
unaccented.

Note that the output string will also be NFKD-normalized.

Example:

1) First, insert a new element which has accents in the nie:title. In the
example we insert the word 'école' which in UTF-8 NFC looks like
"0xC3 0xA9 0x63 0x6F 0x6C 0x65":

    $ tracker-sparql -u -q "
        INSERT { <abc> a         nie:InformationElement .
                 <abc> nie:title 'école' }"

2) Second, get hexdump of querying nie:title, we should get the original string
in UTF-8 and NFC normalization:

    $ tracker-sparql -q "
        SELECT ?title
        WHERE { <abc> nie:title ?title }" | hexdump
    0000000 6552 7573 746c 3a73 200a c320 63a9 6c6f
    0000010 0a65 000a
    0000013

Or, without the hexdump...

    $ tracker-sparql -q "
        SELECT ?title
        WHERE { <abc> nie:title ?title }"
    Results:
      école

3) Last, apply the unaccenting method. The expected string should look like
"0×65 0×63 0x6F 0x6C 0×65" (i.e. without the combining diacritical mark):

    $ tracker-sparql -q "
        SELECT tracker:unaccent(?title)
        WHERE { <abc> nie:title ?title }" | hexdump
    0000000 6552 7573 746c 3a73 200a 6520 6f63 656c
    0000010 0a0a
    0000012

Or, without the hexdump...

    $ tracker-sparql -q "
        SELECT tracker:unaccent(?title)
        WHERE { <abc> nie:title ?title }"
    Results:
      ecole