v0.1.18 Better import / export, preferred poles added, fixed bug in align and bertinCluster

[markheckmann]

• saveAsExcel can export a list of grids now (feat: save gridlist in Excel via saveAsExcel() #67)
• saveAsWorksheet adds a grid as a new sheet to a openxlsx Workbook object.
• makeGrid and randomGrid can add construct pole preference.
• importExcel now also understands the long format (feat: importExcel() should support a long format like saveAsExcel() #65) and can import from several sheets at once (feat: importExcel can read several sheets at once as gridlist #68)
• importDataframe converts a dataframe into a repgrid. Three different formats can be read in. See the sample
  dataframes df_element_columns, df_construct_columns, and df_long (feat: simple way to create grid from dataframe #61)
• saveAsExcel now supports output in wide and long format. The output is also formatted now (feat: saveAsExcel() should support a long format as well #64)
• bertinCluster: now restores the original par() settings after changing the plot layout (bug: bertinCluster() changes the layout but does not restore the par() settings #63)
• importTxt reads preferred poles from section PREFERRED, importExcel reads rightmost column preferred_poles (feat: add construct pole valence (positive/negative/neutral) to repgrid object #57)
• preferredPoles sets the preferred construct poles, preferredPolesByIdeal sets the preferred pole bases on the
  ideal elements ratings, alignByPreferredPole aligns constructs by pole preference (feat: add construct pole valence (positive/negative/neutral) to repgrid object #57)
• biplot3d: New args e.sphere.show, e.labels.show, c.axis.show. c.sphere.show. Construct spheres now hidden
  by default. Construct axes start at origin (biplot3d: parameter to select which e and c to show #9, biplot3d - axes through origin #25)
• print.distance: fix docs for cutoffs arg (invert cutoff arg in print.distance  #18)
• distanceHartmann: change default for method arg to simulate (distanceHartmann method arg has wrong default #19)
• fix bug in align which caused constructs to disappear and subsequent bugs in bertinCluster and cluster (Strange behaviour when working with clusters #22, Issue with cluster #31)