[Taler] Taler wallet library dependencies

[Oliver Broome]

Evening, all!

After getting GNUnet to compile successfully with the newly added wallet
option (thanks again, Christian!), I am currently integrating the Taler
wallet library.

Here's a couple of snags I ran into:
 - the config script checks for libgnurl, libcurl, libmicrohttpd and
postgresql tools and does not continue if they aren't present
 - all source files included in the wallet set try to include the
original GNUnet library headers instead of the wallet-specific one
 - I had to comment out the command line option detail function to get
the library to compile and am still left with a few compiler warnings,
although I'm not sure how serious they are. (they seem to mainly involve
configuration detail pointers and implicit function declarations)

I'm not really confident with the whole build tooling and the project
structure yet, but I will commit my modifications (assuming it is okay
for me to do so?) to the Taler repository as soon as I have something
more sophisticated than commenting the offending sections out and
replacing stuff manually.

So long,

Oliver