taskbrowser: allow relocation/renaming of the taskbrowser history file using the ORO_TB_HISTFILE environmnent flag

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
Merge pull request #16 from orocos-toolchain/relocate_taskbrowser_history

taskbrowser: allow relocation/renaming of the taskbrowser history file